Authority and medical diagnosis

Medical diagnosis these days is not as straightforward as it seems. Doctors still diagnose, but so do a great many people who previously didn't - wellness influencers, misinformation peddlers, users of the many kinds of medical tests available to the public - and then there's the advent of AI and machine learning diagnostics. So what exactly does diagnosis mean today? And what implications do emerging technologies have for the kind of authority traditionally seen as exclusive to the medical profession?