MacCatalyst, UIScene and the green zoom/fullscreen button

Please show me where I’ve gone amiss in MacCatalyst and UIScenes with regard to the macOS green zoom/fullscreen button.

1. Originally the MacCatalyst App used a secondary AppKit bundle for its NSWindow work, but at some point in time AppStore Connect complained about this secondary bundle which prevented new App uploads.

2. To continue receiving green button notifications I switched to UINSWindow. That worked.

3. Now that I’m forced to use UIScenes I’m in a pickle: a click on the green button forces an automatic jump to fullscreen, nothing I can do about it AFAIK.

4. A poor, poor compromise would be to disable the green button but I have no idea how even to do that.

5. I’d like my App to exist in two states, any suggestions?

Thanks.