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`.
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. But - it's not really useful for the most common HDR tasks at the moment.
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. But - it's not really useful for the most common HDR tasks at the moment.