The plugin is not maintained anymore.
Don’t know how big a hurry or what your Linux skill level is but there is a new installer that should be packaged soon with Plex that might be able to update without destroying your setup.
Otherwise, if you track down where Plex was installed you can follow the directions on how to create an override.conf file and continue on with your current setup.
Lastly there are youtube videos on omv/plex/docker like techno dad life https://www.youtube.com/watch?v=BNfk7ji4oh4 that can get you up and running.
