Wireless CarPlay (having been used) prevents AppleWatch from ringing

After a long exhausting period of try and error with lots of configurations it became clear:

The error occurs when the iPhone has been used with Wireless CarPlay (in my case in a 2020 BMW i3). After having been used in the car incoming calls afterwards are only ringing on the iPhone but no longer on the Apple Watch. Only switching off and on makes the iPhone forget the Wireless CarPlay. This problem started with iOS 14/watchOS 7.

Apple should get to know this soon and starting to fix it.

[Posted this hereby again because it is not possible to change the subject of an older post. With this subject the informations can be found better by other users.]