Battery health
When you FaceTime & charge your phone at the same time can that make you maximum capacity drop?
iPhone XR, iOS 14
No. There are several other factors that affect Battery Health and one of them is time. Any battery will lose Capacity as time elapses and it is used. This is the nature of today's batteries in the technological devices. FaceTime while charging has very little to do with it.
Axel F.