Okay, I may be extremely stupid, but a problem I ran into while messing with settings was that selecting fullscreen would make the game's window so wide that the setting to undo my actions would be off the screen and thus unreachable. Might be something with just my terrible hardware, might be something that can be observed elsewhere. Current attempts to fix the issue by deleting the saved settings did not prove fruitful, so I'm gonna check if deleting the whole-ass game folder and reinstalling, then pasting the copied save back in does the trick. Will update with results. Update: somethin went wrong and I had to start the save from scratch, but I did get the screen to finally be the right size, so there's that.