Wait, iphones now support detection of finger hover? I remember hearing about iOS introducing software support for this, presumably for when the hardware can catch up. But never heard of it actually being implemented.
There's an API in iOS/iPadOS named UIHoverGestureRecognizer, but it only detects hover from cursors and from the Apple Pencil. The Apple Pencil hover is neat and actual "hover" detection in the way you're thinking; it can be detected up to 12mm away from the screen. But right now there's no actual detection for finger hover, even though Apple patented a technique for it almost 10 years ago.
I think this is more of an Apple specific hack to get latency down; boot the cameras up as early as possible.
Of course not. Only tapping. But the camera hardware gets booted up as soon as you tap the icon, without waiting to see if the tap is a swipe, and without waiting for you to lift your finger (which is when other apps would open).