120Hz is very dark due to ultra low Backlight Brightness.
Although I like this backlight “dark mode”, as an option, of course, for dark games and movies.
i.e. Try Elite Dangerous, with low backlight, and increase contrast on 120hz, and compare it to 90hz, looks almost oled.
It’s great for games like LOW-FI, Vader Inmortal, Face your Fears, Paranormal Activity, Five Nights, Karnage Chronicles, also it’s great for movies in dark theaters.
Could you add this option for other Hz’s and other headset models?
You should also consider that this backlight brightness problem could be a consequence of the faster refresh rate imposed to the panels, faster refresh/backlight strobing out of the specs of the original panel performance could cause a lesser backlighting, so it could be impossible to have it set to the normal values if operating at 120 Hz.