Hi Simon This is embarassing but I found now what was the issue. There is one package that I installed some months ago that was not from Debian repos and for some reason it installs /lib/libusb. It's not even a deb file which is why dpkg-query does not know about it.
The package in question is xiAPI, from ximea, a company for microscope cameras https://www.ximea.com/support/wiki/apis/xiAPI . Without the whole working from home thing, I would have never have installed on my computer. I'm very sorry for the noise. Thank you for the help, it was the process of answering your questions, and searching for other libs that dpkg did not know about, that made me remember this. David
