I have installed the Plex app on my Samsung TV and I have access to Plex media server.
Same thing on my Sonos speaker.
What I’m wondering is why both Sonos and the TV can’t see the Plex DLNA server.
Plex server runs on QNAP NAS which has also its own DLNA server enabled and the Samsung TV let me navigate through the media on that server.
I also have a LG TV and also there the NAS DLNA server is visible but not the Plex one.
The simple check… did you enable the DLNA server on your PMS?
If you setup a Plex Home, the DLNA server will be disabled by default (DLNA server is tied to your admin account which will conflict with setting up restricted accounts for kids etc.)
Settings > [Server Name] > DLNA > Enable the DLNA server
You might be getting some error in the logs.
Since QNAP and Plex are sharing the same IP, you can’t have two DLNA servers running at the same time.
Disable both DLNA servers, and then enable it only on Plex. That should work.