The symptom
The game runs smoothly while you stand still, but your FPS drops to single digits every time you move the mouse.
The cause
Kefir says this is caused by an excessively high mouse polling rate.
The fix
- Open your mouse configuration app (Logitech, Razer, Bloody and so on), find the Polling Rate setting and lower it.
- If the stuttering continues:
- update your graphics card drivers
- update your BIOS, especially on a 13th or 14th Gen Intel processor
- turn off third-party overlays such as Discord or GeForce Experience
Also compare your PC with the system requirements.