Apple support can view a live stream of your iPhone screen. They used this to confirm what the author saw in their iCloud account.

Really? Where can I read more about this?

It's similar to screen sharing over FaceTime. You first have to accept it, afterwards the technician can see a video stream of your phone and tell you where you have to click. They can't directly interact with your phone.

Googling a bit yields no results. I had them do this to me though. I think it’s not anywhere in settings. They can request this remotely.