Quote
Should I set it to rgb 8-bit, 444 8-bit or 422 12-bit? I'm using PowerDVD 18 on my pc connected to lg oled c8 via hdmi
Most of HDR videos are still encoded with 10 bit color depth and applied 4:2:0 chroma sampling.
Your proposed configurations are bit excessive, and might requier more video conversion while displaying if you set the output as 12-bit color depth, or 4:4:4 (no chroma subsampling).
I will make my display output consistent with what videos I have as possible.
BTW, I think no 8 bit color depth display configuration can present HDR effect.