If you have the Keep Normal Photo enabled, when you get a duplicate one will be HDR, indicated on the white space above the photo, and the other will be the non HDR with nothing in the white space above. If you do not have the duplicate photo enabled you will never see the HDR in the white space regardless of whether it’s an HDR photo or not.
It does not not always take an HDR photo, some will be normal. The background and subject determine this. In my apartment it has been easy to force the camera to take an HDR photo by taking a picture of a wall or part of a room with lamps that are on. It’s easy to tell then which is which because the HDR photo smooths out the glare of the light from the lamps and balances the picture out. The non HDR photo has a lot of glare from the lamps. It’s pretty easy to see.
The other way to force an HDR photo is to turn Smart HDR off but leave the duplicate enabled, you’ll need the duplicate to see the identifying HDR on that one photo. Then on the camera you will see HDR as an option. If you tap it you’ll get a line through it disabling it. If you leave it alone it should take the photo in HDR mode. With Smart HDR the camera decides when to use that and when not, that’s why not all photos will be HDR. But as I did in my apartment you can take a picture with a bright light, the sun or some reflective surface, facing you and it will. It does for me every time and it’s easy to see how much glare there is in the normal photo versus the HDR one.
Now prior to 12.0.1 HDR did not function at all on my Max but works extremely well now.