Si tacuisses... If the goal is to improve on merge conflicts, supporting trailing commas like JSON5 does, is very welcome. One day your old tools will support improved modern formats as well. I for one welcome, that Apple chose the improved format of JSON for the project files right away, instead of changing first to something outdated and then later change it again to the right format for the job.

Answering my own question here just in case someone reads this with the same problem. In my case the problem was, that I was not aware, that a collegue of mine not only converted from AppDelegate to SceneDelegate, but also converted the app to a SwiftUI app. DUH! In case of a SwiftUI App the deeplink will be sent to the  swiftUI view in the WindowGroup, inside the body of the SwiftUI.App! So just adding an onOpenURL() modifier is enough to receive the deeplink event, when the app is running in the background. Case closed. :-)