It seems that DV is the issue.
When I watch the exact same file on through the Kodi app on my TV it works perfectly.
I don't really know why Jellyfin uses Dolby Vision while Kodi uses HDR on the exact same file?
Here are two comparison images. The first shows the washed out, wrong picture which I get when watching it with Jellyfin and the second one when watching it with Kodi:
When I watch the exact same file on through the Kodi app on my TV it works perfectly.
I don't really know why Jellyfin uses Dolby Vision while Kodi uses HDR on the exact same file?
Here are two comparison images. The first shows the washed out, wrong picture which I get when watching it with Jellyfin and the second one when watching it with Kodi: