Try it with different monitors you have. The current nVidia Linux drivers only has BGR output for 10bpp, which works on TVs and OLEDs but not most LCDs monitors.

My monitors (InnoCN 27M2V and Cooler Master GP27U) require RGB input, which means it's limited to 8bpp even with HDR enabled on Wayland. There's another commentator below who uses a Dell monitor and manages to get BGR input working and full HDR in nVidia/Linux.