At the end I found out that the generated APNs certificate is invalid when Mac Catalyst is enabled for the app. Completely frustrated by the fact that the APNs cert was invalid, I have tried to disable the Push Notifications for the app and that could not be done because the Mac Catalyst was enabled. I then disabled the Mac Catalyst and tried to generate again a new APNs certificate with the result of getting a valid certificate. Then there may be something broken on Apple side when generating an APNs certificate with the Mac Catalyst enabled.

I am experiencing exactly the same and I cannot find a valid solution to resolve this. Similarly to d.jeon, this issue manifested with the iOS15 and Xcode 13.0. Is it an iOS 15 bug? And is it expected to get fixed by Apple? Thank you for your response.

Apple, please, prioritise this issue: It is slowing down the developing/debugging process. Thanks!

This turned out to be an erroneous handling in the implementation of func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) of UITabBarControllerDelegate. Thus this all question can be ignored. Apologies.