I changed from a french keyboard to a german keyboard, and changed the default keyboard language. When I changed that back, the MSFS was starting up.
Thanks for your tips which started me thinking what I really changed lately
PS: the Logitech G Hub mentioned in the support document is no more a problem (the document is from august 2020), but that gave me the right idea. Now I have to find a way to use the german keyboard and the MSFS installed with a french one…