Fastsync is NVidia's new "trick" for people who like to play on high FPS (no V-sync), but hate the tearing. It really does not help if your game plays below 60 FPS, which is what G-sync is used for.

Fastsync is software induced, versus G-sync which requires a special monitor with a chip built in.

CPU = i9 11900K
GPU = RTX 3080 Ti
Monitor = ASUS ROG Swift PG32UQX 2160p G-sync