feat(iOS): Enable synchronous screen shadow state updates by default (#3931)

## Description

This PR changes the default value for `synchronousScreenUpdatesEnabled`
flag to `true`

## Changes

Updated default values for the flag in native hierarchy & JS.

## Before & after - visual documentation

N/A

## Test plan

See #3282

## Checklist

- [ ] Included code example that can be used to test this change.
- [ ] For visual changes, included screenshots / GIFs / recordings
documenting the change.
- [ ] For API changes, updated relevant public types.
- [ ] Ensured that CI passes

---------

Co-authored-by: Claude Opus 4.6 (1M context) <[email protected]>

Author: kmichalikk

FabricExample/App.tsx

@@ -1,7 +1,7 @@
 import App from '../apps';
 import { featureFlags } from 'react-native-screens';
 
-featureFlags.experiment.synchronousScreenUpdatesEnabled = false;
+featureFlags.experiment.synchronousScreenUpdatesEnabled = true;
 featureFlags.experiment.synchronousHeaderConfigUpdatesEnabled = true;
 featureFlags.experiment.synchronousHeaderSubviewUpdatesEnabled = true;
 featureFlags.experiment.androidResetScreenShadowStateOnOrientationChangeEnabled =

apps/src/tests/issue-tests/Test2543.tsx

@@ -89,7 +89,6 @@ function FormSheet({ route }: StackNavigationProp) {
       </Text>
       <View
         style={{
-          flex: 1,
           alignItems: 'center',
           justifyContent: 'center',
           height: 180,
@@ -100,7 +99,6 @@ function FormSheet({ route }: StackNavigationProp) {
       </View>
       <View
         style={{
-          flex: 1,
           alignItems: 'center',
           justifyContent: 'center',
           height: 180,
@@ -112,7 +110,6 @@ function FormSheet({ route }: StackNavigationProp) {
       </View>
       <View
         style={{
-          flex: 1,
           alignItems: 'center',
           justifyContent: 'center',
           height: 200,

ios/RNSScreen.mm

@@ -103,6 +103,7 @@ - (void)initCommonProps
   _sheetsScrollView = nil;
   _sheetContentHeight = 0.0;
   _markedForUnmountInCurrentTransaction = NO;
+  _synchronousShadowStateUpdatesEnabled = YES;
 }
 
 + (RNSViewInteractionManager *)viewInteractionManagerInstance

src/fabric/ModalScreenNativeComponent.ts

@@ -121,7 +121,7 @@ export interface NativeProps extends ViewProps {
   leftScrollEdgeEffect?: CT.WithDefault<ScrollEdgeEffect, 'automatic'>;
   rightScrollEdgeEffect?: CT.WithDefault<ScrollEdgeEffect, 'automatic'>;
   topScrollEdgeEffect?: CT.WithDefault<ScrollEdgeEffect, 'automatic'>;
-  synchronousShadowStateUpdatesEnabled?: CT.WithDefault<boolean, false>;
+  synchronousShadowStateUpdatesEnabled?: CT.WithDefault<boolean, true>;
 }
 
 export default codegenNativeComponent<NativeProps>('RNSModalScreen', {

src/fabric/ScreenNativeComponent.ts

@@ -121,7 +121,7 @@ export interface NativeProps extends ViewProps {
   leftScrollEdgeEffect?: CT.WithDefault<ScrollEdgeEffect, 'automatic'>;
   rightScrollEdgeEffect?: CT.WithDefault<ScrollEdgeEffect, 'automatic'>;
   topScrollEdgeEffect?: CT.WithDefault<ScrollEdgeEffect, 'automatic'>;
-  synchronousShadowStateUpdatesEnabled?: CT.WithDefault<boolean, false>;
+  synchronousShadowStateUpdatesEnabled?: CT.WithDefault<boolean, true>;
   androidResetScreenShadowStateOnOrientationChangeEnabled?: CT.WithDefault<
     boolean,
     true

src/flags.ts

@@ -1,4 +1,4 @@
-const RNS_SYNCHRONOUS_SCREEN_STATE_UPDATES_DEFAULT = false;
+const RNS_SYNCHRONOUS_SCREEN_STATE_UPDATES_DEFAULT = true;
 const RNS_SYNCHRONOUS_HEADER_CONFIG_STATE_UPDATES_DEFAULT = true;
 const RNS_SYNCHRONOUS_HEADER_SUBVIEW_STATE_UPDATES_DEFAULT = true;
 const RNS_ANDROID_LEGACY_TOP_INSET_BEHAVIOR_DEFAULT = false;