I also reinstalled VC1 which should use the same engine. VC1 runs at a steady 60FPS.

I'd be very hard-pressed to call Windows 11 an "upgrade" of any kind. Were I you, I'd revert back to Windows 10.

Originally posted by Ric_Reborn:

I finished the game recently using Win 11, I don't believe the OS could be related to the issue.

so the problem is driver tried DDU and reinstall driver again if it still having issue then find the old stable driver if problem still there may be something wrong in your pc

thanks a lot for all your responses. I did not expect a live community for a years old anime game. :D
The issue comes from 2 aspects:
1. Upon my recent PC case cleanup, the GPU was in bad contact. Somehow, it does not affect too much for my usual games like R6S and CS2. I noticed it rather accidentally reinstalling GPU drivers and it was telling me the GPU was running at x4 or x8. So took the GPU out clean the slot and contact.
2. Unlike VC1, this game is very inefficient on AMD cards. It can still run and looks fairly smoothly at 40-50ish FPS in some missions and cut scenes, on worst cases. But if your machine has some other issues, which in my case, is bad GPU contact. It will not run well.

Here I also found a few threads saying they are suffering bad FPS using AMD cards. But actually even RX470 can do it well.

Originally posted by TheAspieFox:

I'd be very hard-pressed to call Windows 11 an "upgrade" of any kind. Were I you, I'd revert back to Windows 10.

IT DOESNT MATTER

Originally posted by ReichsKebab:

thanks a lot for all your responses. I did not expect a live community for a years old anime game. :D
The issue comes from 2 aspects:
1. Upon my recent PC case cleanup, the GPU was in bad contact. Somehow, it does not affect too much for my usual games like R6S and CS2. I noticed it rather accidentally reinstalling GPU drivers and it was telling me the GPU was running at x4 or x8. So took the GPU out clean the slot and contact.
2. Unlike VC1, this game is very inefficient on AMD cards. It can still run and looks fairly smoothly at 40-50ish FPS in some missions and cut scenes, on worst cases. But if your machine has some other issues, which in my case, is bad GPU contact. It will not run well.

Unlike VC1, this one uses Denuvo after all those years. Might also come into play.
A lot of buddies have general performance issues after the last W10 update (or worse, getting forced into W11). For me, even a driver clean up and factory installation of AMD drivers hasn't helped. The same games run fine under Mint though