Right, I was typing it in all caps, but the problem is that it's just not letting me press enter at all. But I think I know what's going on, I was running the game from the itch.io app and that probably screwed up unity's file permissions. Going to try running the .app directly to see if that fixes it.
Yep it was the itch.io app sandbox that was causing it, phew!
Might be nice to add a note to the game page that the app sandbox doesn't work with this game, at least on macOS - it was a very bizarre and frustrating game-breaking behavior (and one which would be difficult to fix).