Thank you!
I had to make it quit the program instead of just returning to the main menu because of potential problems with the save file. I don't think it's that much of an issue, as you can't really use main menu for anything other than starting a new run, which you can do through the "end run" button.
The fullscreen thing is a bug with the library we're using for graphics (it nukes all fucking target textures for some reason TwT), not with the game per se (though I suppose I should've addressed it myself). Windows version of 2.0 will be using a different graphics backend so the issue will hopefully be fixed.