I’ve been using an older version of SpecialK with the game and up until a few months ago it was working great to fix the framerate issues with Windows 10 v2004 but now it no longer seems to work. The framerate seems to fluctuate between 22 & 25 fps instead of the 30fps i was getting with it before. I thought i should try updating to the latest version but it doesn’t seem to be injecting into the game now. I cannot pull up the config menu & i can tell it’s not working as i have it set to hide the mouse cursor as it’s not used in game and it remains visible.
Probably best to restore the old version of SK that you were using. Some of the older mods and whatnot might not always function as good in newer versions of SK.
As to what’s causing the FPS to fluctuate, if not the game and SK have changed then the only possible reason is Windows or the display drivers.