Why camera taking 2 copies at a time? I'm using Asus Zenfone Max Pro M2 with Android Pie. 
So when I take a shot from default camera it does saving two copies at a time. Same for front camera.
Some cameras allow repeated captures if the button is depressed longer. See your manual for settings about the "Continuous Shot" setting, since it may be a form of "burst mode". My Samsung (sorry my experience is not with Zenfone) allows for "burst mode" to allow the camera itself to take a short burst of images, selecting its choice of "best", but keeps the others for any personal preference otherwise. Your phone may do similar.