diff --git a/react/features/base/components/context-menu/ContextMenuItemGroup.js b/react/features/base/components/context-menu/ContextMenuItemGroup.js
index 1e59eb8ef..406962faa 100644
--- a/react/features/base/components/context-menu/ContextMenuItemGroup.js
+++ b/react/features/base/components/context-menu/ContextMenuItemGroup.js
@@ -2,14 +2,15 @@
 import { makeStyles } from '@material-ui/core';
 import React from 'react';
 
-import ContextMenuItem, { type Props as Action } from './ContextMenuItem';
+import ContextMenuItem from './ContextMenuItem';
+
 
 type Props = {
 
     /**
      * List of actions in this group.
      */
-    actions?: Array<Action>,
+    actions?: Array<Object>,
 
     /**
      * The children of the component.
diff --git a/react/features/base/components/context-menu/useContextMenu.js b/react/features/base/components/context-menu/useContextMenu.js
index 5e43d3bc1..84d7c14e0 100644
--- a/react/features/base/components/context-menu/useContextMenu.js
+++ b/react/features/base/components/context-menu/useContextMenu.js
@@ -4,12 +4,7 @@ import { useCallback, useRef, useState } from 'react';
 
 import { findAncestorByClass } from '../../../participants-pane/functions';
 
-type NullProto = {
-    [key: string]: any,
-    __proto__: null
-};
-
-type RaiseContext = NullProto | {|
+type RaiseContext = {|
 
     /**
      * Target elements against which positioning calculations are made.
@@ -22,7 +17,7 @@ type RaiseContext = NullProto | {|
     entity?: string | Object,
 |};
 
-const initialState = Object.freeze(Object.create(null));
+const initialState = Object.freeze({});
 
 const useContextMenu = () => {
     const [ raiseContext, setRaiseContext ] = useState < RaiseContext >(initialState);
diff --git a/react/features/base/dialog/components/native/InputDialog.js b/react/features/base/dialog/components/native/InputDialog.js
index 59f1f6e93..0ee43f76c 100644
--- a/react/features/base/dialog/components/native/InputDialog.js
+++ b/react/features/base/dialog/components/native/InputDialog.js
@@ -70,7 +70,8 @@ class InputDialog extends BaseDialog<Props, State> {
         super(props);
 
         this.state = {
-            fieldValue: props.initialValue
+            fieldValue: props.initialValue,
+            submitting: false
         };
 
         this._onChangeText = this._onChangeText.bind(this);
diff --git a/react/features/base/media/components/native/VideoTransform.js b/react/features/base/media/components/native/VideoTransform.js
index cb7250128..038449895 100644
--- a/react/features/base/media/components/native/VideoTransform.js
+++ b/react/features/base/media/components/native/VideoTransform.js
@@ -1,6 +1,5 @@
 // @flow
 
-import type { PanResponderInstance } from 'PanResponder';
 import React, { Component } from 'react';
 import { PanResponder, PixelRatio, View } from 'react-native';
 import { type Dispatch } from 'redux';
@@ -119,12 +118,12 @@ class VideoTransform extends Component<Props, State> {
     /**
      * The gesture handler object.
      */
-    gestureHandlers: PanResponderInstance;
+    gestureHandlers: Object;
 
     /**
      * The initial distance of the fingers on pinch start.
      */
-    initialDistance: number;
+    initialDistance: ?number;
 
     /**
      * The initial position of the finger on touch start.
@@ -628,7 +627,10 @@ class VideoTransform extends Component<Props, State> {
             this._onGesture('press');
         }
         delete this.initialDistance;
-        delete this.initialPosition;
+        this.initialPosition = {
+            x: 0,
+            y: 0
+        };
     }
 
     _onStartShouldSetPanResponder: () => boolean;
diff --git a/react/features/base/media/constants.js b/react/features/base/media/constants.js
index fafdbe757..a54349732 100644
--- a/react/features/base/media/constants.js
+++ b/react/features/base/media/constants.js
@@ -17,7 +17,7 @@ export type MediaType = 'audio' | 'video' | 'presenter';
  *
  * @enum {string}
  */
-export const MEDIA_TYPE: { AUDIO: MediaType, PRESENTER: MediaType, VIDEO: MediaType} = {
+export const MEDIA_TYPE = {
     AUDIO: 'audio',
     PRESENTER: 'presenter',
     VIDEO: 'video'
diff --git a/react/features/base/react/Types.js b/react/features/base/react/Types.js
index c2e07b5d4..417bfe103 100644
--- a/react/features/base/react/Types.js
+++ b/react/features/base/react/Types.js
@@ -1,6 +1,6 @@
 // @flow
 
-import type { ComponentType, Element } from 'react';
+import type { ComponentType } from 'react';
 
 /**
  * Item data for <tt>NavigateSectionList</tt>.
@@ -73,7 +73,7 @@ export type Section = {
 
     keyExtractor?: (item: Object) => string,
 
-    renderItem?: ?(info: Object) => ?Element<any>
+    renderItem?: ?(info: Object) => null | React$Element<any>
 
 }
 
diff --git a/react/features/base/react/components/native/Container.js b/react/features/base/react/components/native/Container.js
index 488f603f1..8e098c9a5 100644
--- a/react/features/base/react/components/native/Container.js
+++ b/react/features/base/react/components/native/Container.js
@@ -40,6 +40,8 @@ export default class Container<P: Props> extends AbstractContainer<P> {
             touchFeedback = Boolean(onClick || onLongPress),
             underlayColor,
             visible = true,
+
+            // $FlowExpectedError
             ...props
         } = this.props;
 
diff --git a/react/features/base/react/components/native/LoadingIndicator.js b/react/features/base/react/components/native/LoadingIndicator.js
index bd1332d59..a386e2b69 100644
--- a/react/features/base/react/components/native/LoadingIndicator.js
+++ b/react/features/base/react/components/native/LoadingIndicator.js
@@ -1,11 +1,11 @@
 /* @flow */
 
-import React, { Component } from 'react';
+import React, { PureComponent } from 'react';
 import { ActivityIndicator } from 'react-native';
 
 import { ColorPalette } from '../../../styles';
 
-type Props = {
+type Props = {|
 
     /**
      * The color of the spinner.
@@ -17,14 +17,14 @@ type Props = {
      * prop of the native component.
      */
     size: 'large' | 'small'
-};
+|};
 
 /**
  * An animated, large react-native {@link ActivityIndicator} which is considered
  * a suitable visualization of long-running processes with indeterminate amounts
  * of work to be done.
  */
-export default class LoadingIndicator extends Component<Props> {
+export default class LoadingIndicator extends PureComponent<Props> {
     /**
      * Implements React's {@link Component#render()}.
      *
diff --git a/react/features/base/react/components/native/Modal.js b/react/features/base/react/components/native/Modal.js
index 22c50e60c..cc83f52da 100644
--- a/react/features/base/react/components/native/Modal.js
+++ b/react/features/base/react/components/native/Modal.js
@@ -1,33 +1,11 @@
-// @flow
-
-import React, { Component, type Node } from 'react';
+import React, { PureComponent } from 'react';
 import { Modal as NativeModal } from 'react-native';
 
-/**
- * Type of the props of the component.
- */
-type Props = {
-
-    /**
-     * Children of the component.
-     */
-    children: Node
-
-    /**
-     * NOTE: We pass through all props to {@code react-native#Modal} that are
-     * passed to this component, so we don't list them all here, as that would
-     * be an unnecessary duplication and probably an unmaintained list after a
-     * while.
-     *
-     * See list: https://facebook.github.io/react-native/docs/modal.
-     */
-};
-
 /**
  * Implements a generic Modal (using the built-in Modal component) to share
- * behaviour across modals in the app.
+ * behavior across modals in the app.
  */
-export default class Modal extends Component<Props> {
+export default class Modal extends PureComponent {
 
     /**
      * Implements {@code Component#render}.
@@ -35,6 +13,7 @@ export default class Modal extends Component<Props> {
      * @inheritdoc
      */
     render() {
+        // eslint-disable-next-line react/prop-types
         const { children, ...props } = this.props;
 
         return (
diff --git a/react/features/base/react/components/native/PagedList.js b/react/features/base/react/components/native/PagedList.js
index 7b54d8a54..cf4edfb93 100644
--- a/react/features/base/react/components/native/PagedList.js
+++ b/react/features/base/react/components/native/PagedList.js
@@ -92,6 +92,20 @@ class PagedList extends Component<Props, State> {
     render() {
         const { disabled } = this.props;
         const pages = this.props.pages.filter(({ component }) => component);
+        let children;
+
+        if (pages.length > 1) {
+            children = this._renderPagedList(disabled);
+        } else {
+            children = React.createElement(
+
+                // $FlowExpectedError
+                /* type */ pages[0].component,
+                /* props */ {
+                    disabled,
+                    style: styles.pagedList
+                });
+        }
 
         return (
             <View
@@ -100,16 +114,9 @@ class PagedList extends Component<Props, State> {
                     disabled ? styles.pagedListContainerDisabled : null
                 ] }>
                 {
-                    pages.length > 1
-                        ? this._renderPagedList(disabled)
-                        : React.createElement(
 
-                            // $FlowExpectedError
-                            /* type */ pages[0].component,
-                            /* props */ {
-                                disabled,
-                                style: styles.pagedList
-                            })
+                    // $FlowExpectedError
+                    children
                 }
             </View>
         );
diff --git a/react/features/base/react/components/web/Switch.js b/react/features/base/react/components/web/Switch.js
index 112cdae5e..1a0ade630 100644
--- a/react/features/base/react/components/web/Switch.js
+++ b/react/features/base/react/components/web/Switch.js
@@ -3,7 +3,7 @@
 import Toggle from '@atlaskit/toggle';
 import React, { Component } from 'react';
 
-type Props = {
+type Props = {|
 
     /**
      * ID of the toggle.
@@ -29,7 +29,7 @@ type Props = {
      * The current value.
      */
     value: boolean
-};
+|};
 
 /**
  * Renders a boolean input.
diff --git a/react/features/base/toolbox/components/AbstractButton.js b/react/features/base/toolbox/components/AbstractButton.js
index 2219d0c8a..a4158e294 100644
--- a/react/features/base/toolbox/components/AbstractButton.js
+++ b/react/features/base/toolbox/components/AbstractButton.js
@@ -8,7 +8,7 @@ import { combineStyles } from '../../styles';
 import type { Styles } from './AbstractToolboxItem';
 import ToolboxItem from './ToolboxItem';
 
-export type Props = {
+export type Props = {|
 
     /**
      * Function to be called after the click handler has been processed.
@@ -20,6 +20,12 @@ export type Props = {
      */
     buttonKey?: string,
 
+    /**
+     * An extra class name to be added at the end of the element's class name
+     * in order to enable custom styling.
+     */
+    customClass?: string,
+
     /**
      * Extra styles which will be applied in conjunction with `styles` or
      * `toggledStyles` when the button is disabled;.
@@ -29,7 +35,7 @@ export type Props = {
     /**
      * External handler for click action.
      */
-     handleClick?: Function,
+    handleClick?: Function,
 
     /**
      * Notify mode for `toolbarButtonClicked` event -
@@ -61,7 +67,7 @@ export type Props = {
      * Whether this button is visible or not.
      */
     visible: boolean
-};
+|};
 
 declare var APP: Object;
 
@@ -312,7 +318,6 @@ export default class AbstractButton<P: Props, S: *> extends Component<P, S> {
         const props = {
             ...this.props,
             accessibilityLabel: this.accessibilityLabel,
-            disabled: this._isDisabled(),
             elementAfter: this._getElementAfter(),
             icon: this._getIcon(),
             label: this._getLabel(),
diff --git a/react/features/base/toolbox/components/AbstractToolboxItem.js b/react/features/base/toolbox/components/AbstractToolboxItem.js
index 04d52b90f..2f5034d39 100644
--- a/react/features/base/toolbox/components/AbstractToolboxItem.js
+++ b/react/features/base/toolbox/components/AbstractToolboxItem.js
@@ -86,7 +86,7 @@ export type Props = {
     /**
      * True if the item is toggled, false otherwise.
      */
-    toggled: boolean,
+    toggled: ?boolean,
 
     /**
      * The text to display in the tooltip. Used only on web.
diff --git a/react/features/base/toolbox/components/ToolboxItem.native.js b/react/features/base/toolbox/components/ToolboxItem.native.js
index 819ddf82a..6378bdcfc 100644
--- a/react/features/base/toolbox/components/ToolboxItem.native.js
+++ b/react/features/base/toolbox/components/ToolboxItem.native.js
@@ -74,7 +74,7 @@ export default class ToolboxItem extends AbstractToolboxItem<Props> {
             <TouchableHighlight
                 accessibilityLabel = { this.accessibilityLabel }
                 accessibilityRole = 'button'
-                accessibilityState = {{ 'selected': toggled }}
+                accessibilityState = {{ 'selected': Boolean(toggled) }}
                 disabled = { disabled }
                 onPress = { onClick }
                 style = { style }
diff --git a/react/features/breakout-rooms/components/web/RoomContextMenu.js b/react/features/breakout-rooms/components/web/RoomContextMenu.js
index fc7f091fc..f69fbc4e6 100644
--- a/react/features/breakout-rooms/components/web/RoomContextMenu.js
+++ b/react/features/breakout-rooms/components/web/RoomContextMenu.js
@@ -17,14 +17,14 @@ import { closeBreakoutRoom, moveToRoom, removeBreakoutRoom } from '../../actions
 type Props = {
 
     /**
-         * Room reference.
-         */
+     * Room reference.
+     */
     entity: Object,
 
     /**
      * Target elements against which positioning calculations are made.
      */
-    offsetTarget: HTMLElement,
+    offsetTarget: ?HTMLElement,
 
     /**
      * Callback for the mouse entering the component.
diff --git a/react/features/local-recording/controller/RecordingController.js b/react/features/local-recording/controller/RecordingController.js
index 2065a5647..0910dad9f 100644
--- a/react/features/local-recording/controller/RecordingController.js
+++ b/react/features/local-recording/controller/RecordingController.js
@@ -452,16 +452,16 @@ class RecordingController {
         return result;
     }
 
-    _changeState: (Symbol) => void;
+    _changeState: (symbol) => void;
 
     /**
      * Changes the current state of {@code RecordingController}.
      *
      * @private
-     * @param {Symbol} newState - The new state.
+     * @param {symbol} newState - The new state.
      * @returns {void}
      */
-    _changeState(newState: Symbol) {
+    _changeState(newState: symbol) {
         if (this._state !== newState) {
             logger.log(`state change: ${this._state.toString()} -> `
                 + `${newState.toString()}`);
diff --git a/react/features/overlay/middleware.js b/react/features/overlay/middleware.js
index cc5f023ee..074289994 100644
--- a/react/features/overlay/middleware.js
+++ b/react/features/overlay/middleware.js
@@ -11,6 +11,27 @@ import { setFatalError } from './actions';
 
 declare var APP: Object;
 
+/**
+ * Error type. Basically like Error, but augmented with a recoverable property.
+ */
+type ErrorType = {|
+
+    /**
+     * Error message.
+     */
+    message?: string,
+
+    /**
+     * Error name.
+     */
+    name: string,
+
+    /**
+     * Indicates whether this event is recoverable or not.
+     */
+    recoverable?: boolean
+|};
+
 /**
  * List of errors that are not fatal (or handled differently) so then the overlays won't kick in.
  */
@@ -74,16 +95,14 @@ StateListenerRegistry.register(
 
         return configError || connectionError || conferenceError;
     },
-    /* listener */ (error, { dispatch, getState }) => {
+    /* listener */ (error: ErrorType, { dispatch, getState }) => {
         if (!error) {
             return;
         }
 
         if (typeof APP !== 'undefined') {
-            const parsedError = typeof error === 'string' ? { name: error } : error;
-
             APP.API.notifyError({
-                ...parsedError,
+                ...error,
                 ...getErrorExtraInfo(getState, error)
             });
         }
diff --git a/react/features/participants-pane/constants.js b/react/features/participants-pane/constants.js
index f1210cb70..87eefa0e2 100644
--- a/react/features/participants-pane/constants.js
+++ b/react/features/participants-pane/constants.js
@@ -30,13 +30,7 @@ export type MediaState = 'DominantSpeaker' | 'Muted' | 'ForceMuted' | 'Unmuted'
 /**
  * Enum of possible participant media states.
  */
-export const MEDIA_STATE: {
-    DOMINANT_SPEAKER: MediaState,
-    MUTED: MediaState,
-    FORCE_MUTED: MediaState,
-    UNMUTED: MediaState,
-    NONE: MediaState,
-} = {
+export const MEDIA_STATE = {
     DOMINANT_SPEAKER: 'DominantSpeaker',
     MUTED: 'Muted',
     FORCE_MUTED: 'ForceMuted',
@@ -92,6 +86,7 @@ export const AudioStateIcons: {[MediaState]: React$Element<any> | null} = {
  * Icon mapping for possible participant video states.
  */
 export const VideoStateIcons = {
+    [MEDIA_STATE.DOMINANT_SPEAKER]: null,
     [MEDIA_STATE.FORCE_MUTED]: (
         <Icon
             color = '#E04757'
diff --git a/react/features/reactions/components/native/ReactionEmoji.js b/react/features/reactions/components/native/ReactionEmoji.js
index 85d3c464f..2f61908d0 100644
--- a/react/features/reactions/components/native/ReactionEmoji.js
+++ b/react/features/reactions/components/native/ReactionEmoji.js
@@ -68,23 +68,31 @@ function ReactionEmoji({ reaction, uid, index }: Props) {
                 transform: [
                     { translateY: animationVal.interpolate({
                         inputRange: [ 0, 0.70, 0.75, 1 ],
+
+                        // $FlowExpectedError
                         outputRange: [ 0, coordinates.topY * vh, coordinates.topY * vh, coordinates.bottomY * vh ]
                     })
                     }, {
                         translateX: animationVal.interpolate({
                             inputRange: [ 0, 0.70, 0.75, 1 ],
+
+                            // $FlowExpectedError
                             outputRange: [ 0, coordinates.topX, coordinates.topX,
                                 coordinates.topX < 0 ? -coordinates.bottomX : coordinates.bottomX ]
                         })
                     }, {
                         scale: animationVal.interpolate({
                             inputRange: [ 0, 0.70, 0.75, 1 ],
+
+                            // $FlowExpectedError
                             outputRange: [ 0.6, 1.5, 1.5, 1 ]
                         })
                     }
                 ],
                 opacity: animationVal.interpolate({
                     inputRange: [ 0, 0.7, 0.75, 1 ],
+
+                    // $FlowExpectedError
                     outputRange: [ 1, 1, 1, 0 ]
                 })
             }}>
diff --git a/react/features/toolbox/components/native/ScreenSharingIosButton.js b/react/features/toolbox/components/native/ScreenSharingIosButton.js
index da1a526bb..366df63d4 100644
--- a/react/features/toolbox/components/native/ScreenSharingIosButton.js
+++ b/react/features/toolbox/components/native/ScreenSharingIosButton.js
@@ -143,7 +143,9 @@ function _mapStateToProps(state): Object {
         _screensharing: isLocalVideoTrackDesktop(state),
 
         // TODO: this should work on iOS 12 too, but our trick to show the picker doesn't work.
-        visible: enabled && Platform.OS === 'ios' && Platform.Version.split('.')[0] >= 14
+        visible: enabled
+            && Platform.OS === 'ios'
+            && Number.parseInt(Platform.Version.split('.')[0], 10) >= 14
     };
 }
 
diff --git a/react/features/toolbox/middleware.js b/react/features/toolbox/middleware.js
index a2b6429f9..d4289acc6 100644
--- a/react/features/toolbox/middleware.js
+++ b/react/features/toolbox/middleware.js
@@ -84,16 +84,17 @@ function _setFullScreen(next, action) {
             return result;
         }
 
-        // $FlowFixMe
         if (typeof document.exitFullscreen === 'function') {
             document.exitFullscreen();
 
-        // $FlowFixMe
+        // $FlowExpectedError
         } else if (typeof document.mozCancelFullScreen === 'function') {
+            // $FlowExpectedError
             document.mozCancelFullScreen();
 
-        // $FlowFixMe
+        // $FlowExpectedError
         } else if (typeof document.webkitExitFullscreen === 'function') {
+            // $FlowExpectedError
             document.webkitExitFullscreen();
         }
     }
diff --git a/react/features/video-quality/subscriber.js b/react/features/video-quality/subscriber.js
index 6555b6089..13d762d9d 100644
--- a/react/features/video-quality/subscriber.js
+++ b/react/features/video-quality/subscriber.js
@@ -200,15 +200,16 @@ function _updateReceiverVideoConstraints({ getState }) {
     const sourceNameSignaling = getSourceNameSignalingFeatureFlag(state);
     const localParticipantId = getLocalParticipant(state).id;
 
-    const receiverConstraints = {
-        constraints: {},
-        defaultConstraints: { 'maxHeight': VIDEO_QUALITY_LEVELS.NONE },
-        lastN,
-        ...sourceNameSignaling ? { onStageSources: [] } : { onStageEndpoints: [] },
-        ...sourceNameSignaling ? { selectedSources: [] } : { selectedEndpoints: [] }
-    };
+    let receiverConstraints;
 
     if (sourceNameSignaling) {
+        receiverConstraints = {
+            constraints: {},
+            defaultConstraints: { 'maxHeight': VIDEO_QUALITY_LEVELS.NONE },
+            lastN,
+            onStageSources: [],
+            selectedSources: []
+        };
         const visibleRemoteTrackSourceNames = [];
         let largeVideoSourceName;
 
@@ -267,6 +268,14 @@ function _updateReceiverVideoConstraints({ getState }) {
         }
 
     } else {
+        receiverConstraints = {
+            constraints: {},
+            defaultConstraints: { 'maxHeight': VIDEO_QUALITY_LEVELS.NONE },
+            lastN,
+            onStageEndpoints: [],
+            selectedEndpoints: []
+        };
+
         // Tile view.
         // eslint-disable-next-line no-lonely-if
         if (shouldDisplayTileView(state)) {
diff --git a/react/features/virtual-background/functions.js b/react/features/virtual-background/functions.js
index 655400798..e5f0c6cd2 100644
--- a/react/features/virtual-background/functions.js
+++ b/react/features/virtual-background/functions.js
@@ -34,7 +34,7 @@ export const blobToData = (blob: Blob): Promise<string> =>
     new Promise(resolve => {
         const reader = new FileReader();
 
-        reader.onloadend = () => resolve(reader.result.toString());
+        reader.onloadend = () => resolve(reader.result?.toString());
         reader.readAsDataURL(blob);
     });