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.

What's happening is you are running both screens at 144/120 and your 60 is gonna have vsync and screen tearing issues.

What vsync issues?

Couldn't you stop tearing with a couple lines of code? Don't swap out buffers mid-frame, very simple.

The simple solution doesn't make 144+60 look super smooth, but 120+60 should be almost perfect.

How does wayland handle the hypothetical problem of playing a 24 fps movie split across a 48hz and 60hz display?

(Hint: It’s not possible to solve correctly.)

You joke, but the wayland protocol leaves this up to the compositor. Nothing in the protocol prevents your desktop environment from doing this.

I heard the desktop environmentalists are working on such a project.

It is able to output the high Hz to the display, but the desktop (like window decorations and window dragging) remains at 60 Hz, it looks like. Individual windows can still successfully render at high Hz. Contrast this with Wayland where I've always seen everything go at the high speed, even if I'm using the same DE in both (like Gnome Wayland and Gnome Xorg on the same hardware).

Huh ? It did in 2000.