Prevent iOS Alert and Modal from rendering in the top-left corner

packages/react-native/React/Base/RCTUtils.mm

@@ -7,6 +7,7 @@
 
 #import "RCTUtils.h"
 
+#import <atomic>
 #import <dlfcn.h>
 #import <mach/mach_time.h>
 #import <objc/message.h>
@@ -383,24 +384,26 @@ UIDeviceOrientation RCTDeviceOrientation(void)
 
 CGSize RCTScreenSize(void)
 {
-  static CGSize portraitSize;
-  static dispatch_once_t onceToken;
-  dispatch_once(&onceToken, ^{
+  static std::atomic<CGSize> cachedSize;
+  __block CGSize size = cachedSize.load(std::memory_order_relaxed);
+
+  if (CGSizeEqualToSize(size, CGSizeZero)) {
     RCTUnsafeExecuteOnMainQueueSync(^{
       CGSize screenSize = [UIScreen mainScreen].bounds.size;
-      portraitSize = CGSizeMake(MIN(screenSize.width, screenSize.height), MAX(screenSize.width, screenSize.height));
+      size = CGSizeMake(MIN(screenSize.width, screenSize.height), MAX(screenSize.width, screenSize.height));
+      cachedSize.store(size, std::memory_order_relaxed);
     });
-  });
+  }
 
 #if !TARGET_OS_TV
   if (UIDeviceOrientationIsLandscape(RCTDeviceOrientation())) {
-    return CGSizeMake(portraitSize.height, portraitSize.width);
+    return CGSizeMake(size.height, size.width);
   } else {
-    return CGSizeMake(portraitSize.width, portraitSize.height);
+    return CGSizeMake(size.width, size.height);
   }
 #else
   // tvOS doesn't have device orientation, always return landscape size
-  return CGSizeMake(portraitSize.height, portraitSize.width);
+  return CGSizeMake(size.height, size.width);
 #endif
 }
 

packages/react-native/React/CoreModules/RCTAlertController.mm

@@ -23,6 +23,7 @@ - (UIWindow *)alertWindow
     UIWindowScene *scene = RCTKeyWindow().windowScene;
     if (scene != nil) {
       _alertWindow = [[UIWindow alloc] initWithWindowScene:scene];
+      _alertWindow.frame = scene.coordinateSpace.bounds;
     } else {
       _alertWindow = [[UIWindow alloc] initWithFrame:UIScreen.mainScreen.bounds];
     }