In my case with msfs and my monitor, I turn V-sync on in the sim and set frame limiter in MSFS at 50% refresh, (in my case that is 60hz/ monitor is capable of120hz) in order to eliminate flicker in dark areas of the monitor during night flights when FPS exceeds 60. This will make absolutely no difference or hinder G-sync in any way, on the contrary, it creates steady frame pacing and cadence. Who needs over 60fps in the flight sim anyway?
Why the flicker? Could be a flaw with the monitor/firmware. it is not noticeable in any other game, and not noticeable during flights in daylight. I only use v-sync with MSFS for the aforementioned reason.