Hi,
Unfortunately myself and others have the same issue and it comes down to an i915 Driver issue on Kernel 6.1.x which Unraid 6.12.x uses so im really hoping for a new Unraid release with a newer Kernel but I reckon thats a long way off ๐ข
In the meantime, check out the following post on the Plex forum. As a quick fix you can either disable Tone Mapping or you can downgrade your plex container to the version mentioned in the post below ๐
Hope that helps, at least for while you are away on holidays.
https://forums.plex.tv/t/hdr-tone-mapping-with-hw-transcoding-not-working-for-12900k-cpu-on-pms-version-1-32-5-7210/845595?u=v3nom