fix(ios): default contentInsetAdjustmentBehavior to scrollableAxes on iOS 26+

On iOS 26+, Apple introduced the liquid glass design language with
translucent system chrome (tab bars, toolbars). Scroll views need
contentInsetAdjustmentBehavior set to scrollableAxes to automatically
adjust content insets for this translucent chrome.

This change upgrades the default from "never" to "scrollableAxes" on
iOS 26+ when UIDesignRequiresCompatibility is not YES, affecting:

- RCTEnhancedScrollView initWithFrame:
- RCTScrollViewComponentView updateProps: (upgrades JS default "never")
- RCTScrollViewComponentView prepareForRecycle

Apps that explicitly set contentInsetAdjustmentBehavior to "automatic",
"always", or "scrollableAxes" from JS are unaffected. Apps with
UIDesignRequiresCompatibility=YES retain the current "never" default.

Fixes #57299

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: IsaacIsrael

packages/react-native/React/Fabric/Mounting/ComponentViews/ScrollView/RCTEnhancedScrollView.mm

@@ -31,10 +31,16 @@ + (BOOL)automaticallyNotifiesObserversForKey:(NSString *)key
 - (instancetype)initWithFrame:(CGRect)frame
 {
   if (self = [super initWithFrame:frame]) {
-    // We set the default behavior to "never" so that iOS
-    // doesn't do weird things to UIScrollView insets automatically
-    // and keeps it as an opt-in behavior.
-    self.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
+    if (@available(iOS 26, *)) {
+      NSNumber *compat = [[NSBundle mainBundle] objectForInfoDictionaryKey:@"UIDesignRequiresCompatibility"];
+      if (!compat.boolValue) {
+        self.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentScrollableAxes;
+      } else {
+        self.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
+      }
+    } else {
+      self.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
+    }
 
     // We intentionally force `UIScrollView`s `semanticContentAttribute` to `LTR` here
     // because this attribute affects a position of vertical scrollbar; we don't want this

packages/react-native/React/Fabric/Mounting/ComponentViews/ScrollView/RCTScrollViewComponentView.mm

@@ -436,7 +436,13 @@ - (void)updateProps:(const Props::Shared &)props oldProps:(const Props::Shared &
 
   if ((oldScrollViewProps.contentInsetAdjustmentBehavior != newScrollViewProps.contentInsetAdjustmentBehavior) ||
       _shouldUpdateContentInsetAdjustmentBehavior) {
-    const auto contentInsetAdjustmentBehavior = newScrollViewProps.contentInsetAdjustmentBehavior;
+    auto contentInsetAdjustmentBehavior = newScrollViewProps.contentInsetAdjustmentBehavior;
+    if (@available(iOS 26, *)) {
+      NSNumber *compat = [[NSBundle mainBundle] objectForInfoDictionaryKey:@"UIDesignRequiresCompatibility"];
+      if (!compat.boolValue && contentInsetAdjustmentBehavior == ContentInsetAdjustmentBehavior::Never) {
+        contentInsetAdjustmentBehavior = ContentInsetAdjustmentBehavior::ScrollableAxes;
+      }
+    }
     if (contentInsetAdjustmentBehavior == ContentInsetAdjustmentBehavior::Never) {
       scrollView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
     } else if (contentInsetAdjustmentBehavior == ContentInsetAdjustmentBehavior::Automatic) {
@@ -698,10 +704,16 @@ - (void)prepareForRecycle
   _contentSize = CGSizeZero;
   // Reset contentInset to prevent stale insets leaking into recycled scroll views.
   _scrollView.contentInset = UIEdgeInsetsZero;
-  // We set the default behavior to "never" so that iOS
-  // doesn't do weird things to UIScrollView insets automatically
-  // and keeps it as an opt-in behavior.
-  _scrollView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
+  if (@available(iOS 26, *)) {
+    NSNumber *compat = [[NSBundle mainBundle] objectForInfoDictionaryKey:@"UIDesignRequiresCompatibility"];
+    if (!compat.boolValue) {
+      _scrollView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentScrollableAxes;
+    } else {
+      _scrollView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
+    }
+  } else {
+    _scrollView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
+  }
   _shouldUpdateContentInsetAdjustmentBehavior = YES;
   _isUserTriggeredScrolling = NO;
   CGRect oldFrame = self.frame;