When uploading photos from iOS the filenames are changed from their original filename to a unique identifier. For example IMG_4693.jpg becomes 6BE5D325-20A4-4E14-B369-0910F71903FA.jpeg . Other people have also seen this happen. Example: https://developer.apple.com/forums/thread/665133 or https://stackoverflow.com/questions/59415396/ios-11-safari-input-type-file-renaming-file%29

It seems the only way to avoid this is by uploading from files on the iOS device and not from photos. If you want to upload an image such as IMG_0468.HEIC without iOS converting it to jpg, you also would need to upload the file from files on the iOS. See example: