Okay… just for me to understand. The currend Plex Client 3.13.21 does not realise that he is running on a UHD platform.
I tested yesterday a lot and will run some test with konsole protokolls when i’m alone on my server.
But one thing I can already say. I have the same result with the Plex client PS4pro but NOT the AppleTV4k. AppleTV4k can do it.