This Seeking Tech guide will show you how to play Battlefield 6 at up to 120 fps. To do so, make sure you have a 120 Hz screen.
You then need to do the following:
Use the following video as a visual aide:
Step 1: Go to the Settings menu in Battlefield 6.
Step 2: You then need to select Graphics from the left menu.
Step 3: Lastly, set the Performance Preset setting to Performance. This will allow you to play the game beyond 60 FPS, with the maximum frame rate cap set to 120 FPS.