Unfortunately, there is no master list of the capabilities & limitations of the Plex TV apps. Given the number of manufacturers and models that would probably be impossible to keep current.
Here’s the ones I know about.
One more limitation for Samsung and LG TVs: Enabling image based subtitles, PGS or VOBSUB, forces a video transcode. I do not know if this happens due to a protocol limitation or a limitation of the TV itself.
What codecs are supported will vary by manufacturer. I am not aware of any TV that can direct play TrueHD audio. Expect that TrueHD audio will always be transcoded when using a TV based Plex app.
2020 LG TVs do not support dts audio. LG dropped support starting with either the 2019 or 2020 models. Earlier WebOS models support dts audio.
Regarding transcoded audio & subtitles:
LG and Samsung have the same limitations.
TVs running Android TV, such as Sony, should direct play image and text based subtitles even if the audio is transcoding (i.e. no video transcode). This was resolved with version 8.0 of the Plex for Android / Android TV app last April. FYI, also applies to mobile Android devices (phones, tablets) and Android TV based streamers such as the Nvidia Shield and Amazon FireSticks.
I do not know how other Smart TVs such as Vizio & Roku TVs handle subtitles. You might ask or scan the posts in their sections of the forum.
