Hi
I'm new here and have had trouble with iPhone photo uploading to the site - but I have found a way that works for me with an iPhone 8 and a Macbook
I emailed the photo from my phone to myself, opting to send the file as a SMALL file
From my email, I saved the photo to mt desktop - giving it a name and ".jpeg" suffix
Then just uploaded simply from the "More Reply Options" button at the bottom of the text box, following the instructions
Works for me - hope this helps