I have 2 Roku 4k Ultras but only 1 4k tv, the other 4k ultra was connected to a 1080p tv. I got a new 4k tv so the took our old 4k tv and replaced the 1080p with it… soon as i did the 4k ultra roku that i had connected to the old 1080p would not play 4k HDR movies from plex it would default back to 1080p i could force it but it was not HDR and would sometimes tell me “my server was not powerful enough” message which was BS i know my server is powerful enough to play 4k HDR movies… So i moved the Roku 4K ultra from the other room that works fine and swapped, it played perfect in both places !!! so what was the issue…
Seems the Roku 4K ultra that would not play HDR movies from plex was a model 4660RW , well it would play HDR movies fine from say other apps like Disney + or Netflix on the roku, but just not plex… the other Roku 4K ultra that worked fine against both TVs was a model 4670X, purchased in Jan 2021… so it’s newer , faster processor all that…
So my guess is Plex doesn’t support the 4660RW playing HDR, and there must be some code in the plex app that detects the Roku model and thus forces the movie to start playing at 1080p, if you have 2 versions of the same movie file (1080p and 4K).
So , just word to the wise be careful if you buying any Roku Ultra 4K “expecting” to be able to play 4K HDR movies via plex app on it, you need to get one of the latest models of Roku Ultra 4k
