Before I retired I worked in IT and we had a devil of a time converting HEIC to jpg and other formats. However that was four years ago and while I stay somewhat current I haven't seen any recent problems as long as you use a converter.
You might try a different converter. Microsoft has a free converter for Windows 10 called HEIF Image Extensions. I'd provide a link but I've gotten in trouble before providing external links. But it should be easy to Google.
I misunderstood. I thought your computer was a Windows computer and your phone an iPhone. A converter for Windows isn't going to help on an Apple laptop. I don't know much about Apple products, but I would think you should be able to load the image directly without any converter.
I dug more, it is the HEIC image format. None of the browsers will even display it, so allowing it to upload would be a problem anyway. I have a newer iphone and it doesn't take photos in HEIC format. Maybe you have a setting or something forcing it to do this?