As I understood the article, the problem did not arise when uploading the picture directly from the phone, but in cases in which the picture was first transferr

As I understood the article, the problem did not arise when uploading the picture directly from the phone, but in cases in which the picture was first transferred to a computer (via Airdrop was explicitly mentioned, but could probably also have been a cable connection) and then uploaded from the computer. Whatever conversion the browser on the iPhone (or Safari on macOS, because there are other browsers on computers as well) does or does not do is irrelevant in such a situation.