G-Sync on or off shouldn’t cause any CTDs because it is hardware/software in the GPU and monitor to dynamically change the monitor refresh rate to the FPS output. Windows doesn’t know about G-sync except through NVIDIA Control Panel. MSFS doesn’t know about G-sync.
If you suspect G-sync causing CTDs, then NVIDIA should be contacted for support.
In general, NVIDIA driver problems could potentially cause a CTD if Windows detects a problem (“hardware error” in the Event Log). Windows will kill any graphics apps to restart the driver.
I’ve had G-sync on and V-sync off for almost two years across multiple NVIDIA drivers and MSFS updates without any CTDs attributable to G-sync that I know of.