> It's not an Apple format

Create a HDR HEIC file on anything other than an Apple Device.

Upload it to an Apple Device.

Now use it any way: Forward it, attach it to a message, etc...

This won't work.

It won't ever work because the "standard" is not what Apple implements. They implement a few very specific subsets that their specific apps produce, and nothing else.

Nobody else implements these specific Apple versions of HEIC. Nobody.

For example, Adobe Lightroom can only produce a HEIC file on an Apple device.

My Nikon camera can produce a HDR HEIC file in-body, but it is useless on an Apple device because it's too dark and if forwarded in an iMessage... too bright!

It's a shit-show, comparable to "IPv6 support" which isn't.

That's not an argument. HEIC is to HEVC what WebP is to WebM. The lack of support in other products is due to developers not picking up the pace and sticking with "GIF, JPEG and PNG is good enough".