I keep getting this error whenever I try and run the game or the launcher, and I know this game should work on XP because that's how I played it originally. The GECK seems to work fine though

According to https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-queryfullprocessimagenamea this only works starting in Windows Vista.

Maybe an update changed the system requirements in such a way that the game doesn't work on Windows XP anymore.