Questions about Samsung Odyssey G5

Yes, it can do 120 FPS

No

The Samsung Odyssey G5 monitor, despite being officially labeled as AMD FreeSync Premium, is also compatible with NVIDIA G-Sync. This compatibility is possible if you have an NVIDIA graphics card from the 1000 series or newer. This means you can use the Variable Refresh Rate (VRR) features of both FreeSync and G-Sync on this monitor, as long as you meet the NVIDIA GPU requirements.