I could hardly believe there would not be a topic about this yet, but maybe that means it’s a new issue since the latest release? I couldn’t find anything, at any rate.
I don’t seem to be able to pause the game. P or Pause/Break don’t work, and opening the menu just has the game continuing to run in the background (nor is there a menu option to pause). I don’t know if this is by design, but I doubt it. I would suggest to add a pause option with the P or Pause key, or to just have the game pause automatically when you pull up the menu.