I will also be creating guides for AC Brotherhood, Revelations, and AC3 Remastered, as they all share a common solution, though the fix for this game differs slightly.

This fix has been tested on the Steam Deluxe Version of the game but should work with any base version on any platform.

1. Launch AC2 via Steam or your chosen client.
   
2. Press ALT+TAB to return to your desktop.
   
3. Open Task Manager by pressing CTRL+SHIFT+ESC.
   
4. Navigate to the Details tab.
   
5. Right-click the executable, which should be near the top of the list if sorted alphabetically.
   
6. Select Set Affinity.
   
7. Uncheck the first core in the list (Core 0).
   
8. Click OK.
   
9. You can now close Task Manager and ALT+TAB back into the game, enjoying smoother and more consistent performance! Keep in mind that this game is capped at 60 FPS, so you won’t exceed this limit even on a high refresh rate monitor.

IMPORTANT: This fix needs to be applied every time you launch the game!

I hope this guide helps you resolve any stuttering or low FPS issues in a game that deserves better performance. If it was helpful, please consider marking it as a favorite and leaving a 5-star review. Stay tuned for guides on AC Brotherhood, Revelations, and AC3 Remastered, as they share similar performance issues!