If Plex DLNA doesn’t know your TV, it’ll try to supply the files using a generic profile.
Working out what formats are actually supported via DLNA can be tricky as many vendors don’t enable all formats the TV supports for other apps or via DLNA.
There’s a very, very long post on how to work with DLNA profiles.
To be very open… it’ll probably be easier to get an entry-level streaming box or stick and attach that to your old Samsung…
