UaaL integration to Swift-based apps is not supported.

Without deeper investigation, this fix for iOS13 from newer Unity versions to respect UIScene made FB login window to appear again after the video view.

1. add next function in UnityAppController.mm before a call to didFinishLaunchingWithOptions

#if (PLATFORM_IOS && defined(__IPHONE_13_0)) || (PLATFORM_TVOS && defined(__TVOS_13_0))
- (UIWindowScene*)pickStartupWindowScene:(NSSet<UIScene*>*)scenes API_AVAILABLE(ios(13.0), tvos(13.0))
{
// if we have scene with UISceneActivationStateForegroundActive - pick it
// otherwise UISceneActivationStateForegroundInactive will work
// it will be the scene going into active state
UIWindowScene* foregroundScene = nil;
for (UIScene* scene in scenes)
{
if (![scene isKindOfClass: [UIWindowScene class]])
continue;
UIWindowScene* windowScene = (UIWindowScene*)scene;
if (scene.activationState == UISceneActivationStateForegroundActive)
return windowScene;
if (scene.activationState == UISceneActivationStateForegroundInactive)
foregroundScene = windowScene;
}
NSAssert(foregroundScene != nil, @"No foreground window scene found at startup");
return foregroundScene;
}
#endif

2. in didFinishLaunchingWithOptions replace
_window = [[UIWindow alloc] initWithFrame: [UIScreen mainScreen].bounds];
to:

#if (PLATFORM_IOS && defined(__IPHONE_13_0)) || (PLATFORM_TVOS && defined(__TVOS_13_0))
if (@available(iOS 13, tvOS 13, *))
_window = [[UIWindow alloc] initWithWindowScene: [self pickStartupWindowScene: application.connectedScenes]];
else
#endif
_window = [[UIWindow alloc] initWithFrame: [UIScreen mainScreen].bounds];