Multiple refresh across multiple monitors works fine with xorg + nvidia, I'm doing it now with a 60hz ultrawide LG and a 144hz 1080p ASUS. I'm curious if it's a gnome thing, since I'm running KDE, but it may be that it's forcing the monitors to sync to a specific monitor. I know you can set that in the nvidia-settings panel under xserver xvideo settings. It might be worth turning off gsync to see if it uses the right refresh on each monitor, too.
Doing a brief search I'm finding a bug report of something like this (where it's a mixed environment and it defaults to the lowest common refresh, in this case 60) with mutter in general and the fix, from what I can see, still not fully merged. The workaround was to force the setting through config files rather than the UI.
Doing a brief search I'm finding a bug report of something like this (where it's a mixed environment and it defaults to the lowest common refresh, in this case 60) with mutter in general and the fix, from what I can see, still not fully merged. The workaround was to force the setting through config files rather than the UI.