Maybe DRM Prime has an HDR bug on RPi5
Nope .. at least not one affecting the 40K+ RPi5 users we have (else there'd be more folks showing up with issues).
All the error messages flagged above are normal/harmless, and show it setting an HDR colourspace and 12-bit output. The RPi side appears to be doing everything correctly. I think the solution lies in AVR and/or TV settings, or port combinations.