Since last Autumn (2021) Plex Media Server is not working on my QNAP. I uninstalled and reinstalled Plex with no result. The server was restarted a few times with no result. Also, I stopped and started Plex manually a few times and I had no positive result.
Any hints in your server logs as for why it’s not starting?
I’ve seen cases of very badly corrupted databases which could prevent the server from even starting up properly.