Website Uploader says "Unable to Upload"

I have heard the terms, but I don’t understand them. I never tried to upload any kind of files, or change any photo files. I would always just take a photo with my camera, let my wifi put them in Photos automatically, and I would either upload them as they were or after cropping or brightening them. That’s it. I have the same camera now, but a new iPhone 13 Pro. The iPhone is a disappointment because the web uploader doesn’t like it’s HEIC, so I wanted to go back to my regular camera. But now I can’t get to any of my photos through the web uploader. I can’t choose the camera photos only, because this new screen doesn’t allow me to see my photos.