Came here while searching for information about this issue.
I was so excited to learn that this issue should be tackled in iOS 14.4 that I installed the current Beta on my iP12P
And indeed, something has changed:The HDR highlights are now looking the same (enhanced) in edit and in normal view.
But the midtones still shift and thus it's still very confusing to use the editor to actually edit a photo.
This shift is also visible in a screenrecording:
View attachment 1718555
It's most noticeable when leaving edit mode, because then the picture "jumps" back in an instance, whereas it transitions for a second or so while entering edit mode.
And it's much more obvious if you cover the areas above and below the picture.
I'm a bit surprised that the engineers at Apple didn't catch this.
Hope they will eventually - I love to edit my photos and this makes it a slighlty frustrating experience.
Sidenote: I'd wish there'd be a switch in the editor to quickly toggle between HDR and normal view.
This would make it easier to optimise a photo depending on the targets display capability.
Ideally it would be possible to control both representations independently and save the settings in the photo.
But I guess that would overcomplicate things for many users.