You need to make sure you delete the plex user before reinstall:
userdel plex
I will try that. I have upgraded to OMV 5, then i found some threads on the forum which directed to "rm -rf /var/lib/plexmediaserver". I did that, then i used instructions for installing plex docker i found from google https://dbtechreviews.com/2020…plex-on-openmediavault-5/
Plex is running, but now the problem is Plex, for some reason, cannot see my media folders.
Should i still "userdel plex"?