For anyone else new like me, + and - keys control the speed of the game. Not quite the same as a pause button the way I'd hoped, but it's better than having to always click by cursor.
This is conspicuously absent from the controls, both listed here and the in-game settings. I probably wouldn't have discovered it, except the prequel for this game has it listed on its page, so I had to try. Sure enough, works
