I would suggest starting @ [INFO] Plex, 4k, transcoding, and you - aka the rules of 4k
if your pc is saying it is outputting 8bit then it it is not hdr.
most likely explanation is that your receiver is upscaling to hdr, so the tv only sees what the receiver has upconverted.
I would expect you can disable the upscaling in the receiver options.
you might also check your receiver if it has a “PC” video mode you can enable that might allow the pc to output hdr.
you should also check your video card model if it even supports hdr.
finally, if PMP doesn’t support hdr (I don’t use it so I can’t confirm) then none of that really matters.
