I see that there is a FlatPak of Plex, but searching the forums, it seems that some have had some fairly big issues with it.
One of the advantages of Plex is it’s cross-platform compatibility. I think that a flatpak for both the player and the server would be a good addition.
Plex for Linux and Plex HTPC desktop apps are already available as official Flatpak versions.
See: https://www.plex.tv/media-server-downloads/#plex-app
I guess a PMS Flatpak is less realistic as (a) it implies usage on a desktop machine and (b) applies various restrictions to how the server could operate
