Thank you @ptillisch , this is more complex than I expected!
I read it twice to get an idea, and I will read it several times more.
As soon as I have time for this, I intend to do some experiments.
I would like to see how the different cases manifest themselves on the USB port identification on Windows. And of course the use of the appropriate recovery actions to get back to normal Arduino UNO R4 Wifi use.
Thank you for this complete information.
-jz-