Streaming-Quality issue on Smart TV "Hisense 75U8NQ" on a QNAP TS-451+ (16 GB RAM)

Server Version#: 1.42.2.10156
Player Version#: Plex for VIDAA 5.93.2
Plattform#: V0000.09.01UP0509
Renderer#: WebGL

Hello @ all,
i use Plex since one year and had no problems on an LG Smart TV, PC, Notebook, Tablet and Smartphone.
Now we bought a Hisense 75U8NQ, with preinstalled “Plex for VIDAA” and the quality of videos is really really bad.
I tried to activate “direct stream” and “direct play” in the Plex-Player-Settings, i put the quality on max/original, i changed on Plex Server the transcoding on max quality and later deactivated it (this only thown the message “not enough CPU for transcoding”).
I use a gigabit network, fully connected with cable.
I am sure, the problems is within the Plex Client/server settings, because i can stream the same files with great quality on the TV, if i play the file directly from NAS-folder, without Plex.
On the Client i had to change Video→Qualitysuggestions off, because there was an infinit loading circle.
The videofiles are .avi, .mp4, .mkv

I hope someone can give me a hint or a solution for this.

Thanks for reading and your time :slight_smile: