hi im also on mac, i reused my Sikarugir barrel i made for other windows steam games and it ran perfectly well. But for ZATO alone instead of running steam/steam installer run the ZATO exe, unless you want steam for windows. Video i used to set up the barrel
I also just checked for this comment and it runs via steam for mac, but not as a standalone (what you did). maybe because of the 32bit warning?? but idk why steam can open it and it by itself cant... hope you get to play it its amazing