It would be good if tabBarController.tabBar.isHidden also worked on visionOS.

Never mind. It turns out that all the targets need to have the same product name. The product name defaults to the $(TARGET_NAME). I made sure the bundle names matched, but not the product names.

I'd be much happier if the virtual game controller laid out its controls after a rotation.

Quite frankly, I don't think that replacing the GroupActivity is the right way to reset the canvas in the sample app. The GroupActivity session is the connection over which the applications exchange data. The state of the canvas is the application's responsibility. The example was probably adapted from SharePlay, which is built on top of GroupActivities. SharePlay uses a GroupActivity to exchange data about playback state. The application should not mix into that, and so the application changes the GroupActivity session when the user(s) want to play something different.