I can select a UICollectionView cell in Mac Catalyst. Local notifications also work. I'm running Big Sur, and maybe things have improved in a year.

Quitting Xcode and opening again. Restarting the phone. Cleaning the project from Project menu and selecting Clean Build Folder Once I did all these things, it fixed the issue for me. Sometimes it's the simple things.

As far as I can see openAppWhenRun is static, and is read and opens the app even before perform() is run (if openAppWhenRun is true that is). In other words, openAppWhenRun can not be dynamic. Your variable myNumber is always false at the time the App Intent is run so that is why your app never opens. It would be interesting to see where you set, and changed, the myNumber variable.