Earlier quoted context omitted.
You can enable, yes. But (assuming you're on an LCD display and not an OLED), you're likely still on XRGB8888 - i.e. 8-bit per channel. Check `drm_info`. Also, go to YouTube and play this video: https://www.youtube.com/watch?v=onVhbeY7nLM Do it once on "HDR" on Linux, and then on Windows. The "HDR" in nVidia/Linux is fake. The brightness you see on Plasma or Mutter is indeed related to the HDR support in the driver.…
It's not obvious how to interpret the output. I pasted it into chatgpt and it thinks I am using "Format: ABGR2101010" for both monitors (only 1 has HDR on) so I don't trust it. EDIT: See my sibling comment.
Here's what I'm getting on an RTX 4090 / InnoCN 27M2V and Cooler Master Tempest GP27U.