Hi Hoffman, thank's a lot for your reply. It sounds like, as you write, on the one hand it is possible to code on XCode with C++ as well as on any other IDE and XCode was not obligatory needed for app development for iOS/macOS. But on the other hand Apple was more and more focusing on Swift and you advise to learn Swift instead? I don't have many existing self coded C++ libraries or other stuff that should have been converted, so maybe it would be the best way to start learning Swift and for that, taking a look at Playgrounds? I will give it a try! Thank you.

Dear DTS Engineer, thank you very much for your fast reply and for the links attached. I will review them carefully the next days. What do you basically think about the way I solve the issue with handling multiple root views? Is that a good way for iOS, iPadOS and macOS management of views? When using your example with a wrapping master view "ContentView" over all root views, I don't really have more than 1 root view anymore, but that should be no problem I think. Maybe that's the "normal" way of doing it, when it is needed for a working preview..