> What saddens me the most is to see those kids who grew up with a smartphone in their hand trying to convert a picture by renaming it

Why shouldn't that work? I think it would be pretty great if changing the file extension popped up a helper that asked me if I wanted to convert from HEIC to JPG?

Really, no-one should have to think about file formats when they're trying to do something that has nothing intrinsically to do with file formats.

Seems more like a failure of software engineering, to me.