SOLVED: Jellyfin Playback Error

[xFanexx]

Hello community!
I have a problem with my Jellyfin Server.
If i try to play an 4K movie (lets say Harry Potter) its returns me the following error: "This client isn't compatible with the media and the server isn't sending a compatible media format."

I tried:
- Rebooting
- Changing the decoding settings
- Rebooting the whole server

Config:
- Windows Server 2022
- AMD Ryzen 5 2600
- NVIDIA GeForce GTX 960 4GB
- Jellyfin version 10.8.13
- NVIDIA Driver version 552.12

What can i do that i can finally watch my movies?

I will include FFmpeg logs in this post.

Thanks in advance.