how can you play "it takes two" with a single controller and PC keyboard?

No.  The only controller I have is the one I specifically purchased for the game, which is similar to a Switch controller.  The PC recognizes the controller via Bluetooth.  No problem there.  Also Steam has no problem finding the controller and I can calibrate there, etc.  But there are lots of options for configuration in Steam, and I don't know if some variation of those might work.  I've tried a few.  But I could spend hours randomly trying different combinations, with no guarantee any would eventually work.

I could also connect with a USB port if that might fix the situation.  The controller instructions tell me how to use "D-input Mode" and "X-input Mode", as well as Bluetooth Android Mode.  None of these terms mean anything to me, and there are no instructions on the game which help either.  Neither the game nor Origin itself has a way to search for controlling devices.  The game seems to recognize the keyboard automatically.  But not the controller.