The OMV user forum is full of guides for setting up dockers, including Plex.
The typical procedure to update Plex via docker is to first chose the proper image tag when installing the docker, and then to just restart the container when an update is available.
I suggest using the docker instead of the OMV Plex plugin. But I have a dozen or so dockers running here and running one more or one less doesn’t make a difference in my setting.
