Comment 91 for bug 1968040

I'm not sure why the mode would be limited to 60Hz but you should know that Xorg's multi-monitor support is very limited. It can only update all monitors at the same time at the same rate. So if you have a 60Hz monitor connected then it's possible Xorg will limit all monitors to 60Hz.

Even if all your monitors are the same refresh rate, Xorg is still a menace because it tries to update all of them at the same time even if their clocks aren't in sync. This means you might see tearing.

Wayland solves all of the above.