This sounds as though it should be straightforward, but the simplified shortcut below doesn’t work.
The Turn Focus Mode on/off action accepts variable input; the variables in the list (as far as I can see) match my focus modes; but the shortcut always turns Do Not Disturb On. (This is true even if I remove Do Not Disturb from the list.)
The first two actions (get current focus and turn it off) were added just to make sure a current focus mode being on wasn’t getting in the way somehow. It doesn’t alter the output.