I just found that trying to upload a .heic image to my gallery results in a generic HTTP 500 server error. I suspect it's trying to manipulate the image in some way but doesn't know how to handle the HEIC format.
I'm not asking for proper HEIC support, but maybe just a better error message. In this particular case I'd accidentally picked the wrong format when exporting and simply didn't realise that I had an HEIC file in the first place, so I was a bit clueless as to the actual problem.
I've put a copy of the actual file online in case it's something specific to this particular file.