It runs just fine at 165 hz for me. Given that xrandr and CRTs have been around for a while, and both have supported high refresh rates for a long while, something seems fishy here. Something is probably at fault, but it's not X11.

X11 can't do different hz on different screens. If you have a dual screen setup where one screen is 165 hz and the other is 60 you're SOL.

Works fine for me with 144/120 with the second as 60.

X11 can't fix climate change.