4K HDR plays as 1080p RGB

[amasuke55]

Describe the bug
Playing a 4K HDR file (see screenshot for info on file) through jellyfin on mpv shim results in 1080p resolution window and playback mapped to rgb.
using mpv standalone and dragging the file into it makes it work. But that completely ignores jellyfin in the chain.
I'd have expected that playing the file via directplay from jellyfin to mpv shim would result in the same outcome as playing the file directly in mpv standalone.

I'd greatly appreciate hints or help, hoping it's not exactly a bug but some configuration on my end.

To Reproduce
Steps to reproduce the behavior:
Play 4K HDR video in Jellyfin via MPV Shim through directplay

Expected behavior
MPV should play the video in 4K HDR

Screenshots

Desktop (please complete the following information):

• OS: Windows 10 Pro
• Version: 22H2

Error Messages
No logs as it's not exactly showing an error. But I can provide them if needed.