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.
I connected two portable LCDs I have that support HDR. Both LCDs didn't automatically detect HDR and looked washed out initially. I had to manually change them to HDR. The signal according to the AVR was...
With the HDR off for both the desktop and LCD, the Youtube HDR video at 19s seems flat. I could increase the monitor's brightness to match the planet brightness when HDR is on, but space would be washed out. Of course without HDR, lowering the brightness for darker space results in the planet becoming darker too.
When HDR is off for LCD and desktop I do still see a difference between Youtube's HDR and SDR videos. For example, at the 19s mark I cannot see most of the debris scattering between the viewer and the planet in the SDR video. That should be the case for you too.
*Edit: Strange... one of the monitors states 10bit colors in the link even though the AVR claimed a signal of 12bits. Not sure what to make of that!
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.