I can't change the resolution or switch to full-screen mode

Thanks for checking all of that ZeTerBerk​ 

If you're using an NVIDIA GPU, one workaround reported by other players is to check:

NVIDIA Control Panel > Manage 3D settings > Program Settings > Battlefield 6 > Automatic display switching

If that option is enabled, try setting it to Off, apply the change, then restart the game and test the display settings again.

This isn't a confirmed fix, but it has helped some players with very similar fullscreen/resolution issues.