I fixed that problem. Apparently Windows has it's own version of Python hidden in "WindowsApps". I got rid of it, and now that error is gone, but it's still not working.
Now when I try to play a video it plays for a half a second and then freezes indefinitely. There aren't any errors in the logs when this happens.
EDIT: So, in Plex it freezes as I said, but in MPC-HC, it just doesn't work. The performance monitor shows the SVP Index at a constant 0.5 (normal framerate, since I have RIFE set to x2). Setting the profile back to Automatic works as expected, it's just RIFE that isn't working (both the CUDA version and the normal version of RIFE in MPC-HC, although in Plex, the normal version works, and CUDA version freezes playback).
EDIT 2: I just found the note at the bottom of the wiki page saying it doesn't work for real-time transcoding, which is what I've been testing it with. That's unfortunate. Any plans to make that work? Also maybe getting it to use the tensor cores?