To close this thread, I was eventually able to run the camera. This happened after - at the request of QGYCCD's support - I installed their SDK so I was forced to rebuild from source code afterwards. I can't recall what I did differently, but after that it worked. One possibility is that my first source code build crashed one time and I had to restart it; it continued where it left off, maybe something broke there. It can also be a missed uninstall of the QHYCCD SDK - I can't remember.
I was told that the original PID in dmesg is 0200, afterwards it becomes 0201 (in lsusb for instance).
So, it's a bit of a mystery but it could well be my fault. Thanks for your support.
One very useful link that I found for rebuilding from source code is: gitea.nouspiro.space/nou/astro-soft-build . This builds Ekos and KStars, server and client, all in one go and works great.