I was able to fix the problem by re-installing Xcode from the app store... I had previously updated from the Developer downloads area.

I lost 2 days of work before finally taking the easy way out and upgrading the phone to iOS 16... this is the worst Xcode update in years. My iPhone 8 running 14.8.1 was unaffected?!

Apple is going down the tubes. You can't have 2 versions of Xcode on one machine. This is bull. They better fix that. I need to support 15.x and the only device I have is at 15.7 and cannot be downgraded. This update is garbage.

Actually I don't see that in the release notes - where is it?

This fixed the problem for me. I did not have to implement a UIApplicationDelegate in my SwiftUI app.