The navigation and system bars are transparent when compiling with iOS 15 + Xcode 13. The solution is to explicitly set the color of the navigation controller internal view:
It will be set like this in the core library automatically, in the next version.
B4X:
NavControl.As(NativeObject).GetField("view").As(B4XView).Color = xui.Color_White
It will be set like this in the core library automatically, in the next version.