are you trying on a new board, from scratch, or a board that was already setup with LxQT that you are trying to 'dist-upgrade'?
The initial instructions to get graphics drivers included packages from Debian experimental, and that could be the source of such isssues. If possible , I would recommend to start from scratch , using the latest image, and using the latest instructions on the wiki since all our dependencies are now in sid, and experimental is not needed anymore.
If you cannot restart from scratch, we can try to repair the system by removing all packages from experimental and re-install them.
I haven't turned on my board for a couple of weeks, i will try to upgrade on my side as well to check if everything still works.