I would really appreciate a framework engineer's feedback here. I can't seem to figure out how to solve the issue. I have thought about using a storyboard setup for the app, but this would result in a lot of overhead work. Also, I don't even know if the issue would actually be resolved this way. I simply suspect it would be, since newly created objective c projects (which use storyboards by default) are displayed as you would expect.

Though the reason self.view.window.windowScene.screen.bounds has the same value is probably that the window initialized in the App Delegate still uses the +[UIScreen mainScreen] to set its frame size. Can I somehow access the correct value in the AppDelegate?

I answered the question instead of responding to the comment by mistake, please delete this

The issue seems to originate from a layer above the WindowScene. I checked, and the value reported for self.view.window.windowScene.screen.bounds is the same as for the mainScreen's bounds. Also as mentioned in my question, forcing the window (which is as far as I know the outermost layer I can access) to be a different size doesn't solve the issue. The window itself seems to be clipped inside those 320x480pt bounds.

I have found a workaround for this issue by now - not using any .estimated sizes in the Compositional Layout prevents the unwanted reloads. But the bug causing the issue in the first place wasn't fixed yet. As I am unsure as to where I should file this issue I'm commenting here, hoping that someone can help me out.