Isn’t that because full screen windowed turns g-sync off though? I’ve seen this mentioned elsewhere.
I’ve been looking at this myself as I’m about to take delivery of a new rig with RTX 3080 and the monitor choice is a minefield.
The vast majority of threads I’ve read here and on Reddit tend towards G-Sync working but issues with flicker in menus and when at the limits of the frequency range. Outside of the g-sync certified monitor list I think it’s a risk and even if an owner of a particular monitor tells you it’s fine then it’s no guarantee you’ll have the same experience.
Nvidia does the work to check compatibility for a reason, if the monitor you are looking at isn’t at least G-Sync compatible on the list then I’d say buyer beware.