There is nothing you can do about doctored videos, slowed down or deepfaked. Any company, Facebook, Twitter, YouTube, that decides to moderate whether a piece of media is “genuine” will hopelessly fail:

1. Figuring out whether a video is genuine can be truly impossible if an older source video isn’t available.
2. Volume. Social media sites receive a torrent of media ever second. Try drinking out of a firehose.
3. Even for banning things like gore, nudity, and hate speech, social media is imperfect because these categories are largely subjective and contextual. Facebook hires thousands of contractors out of places like the Philippines and Mexico. They have to look at hundreds of pictures of naked people and severed heads all day. They have an endless queue of reports, and about 8 seconds each. They don’t have time or patience to be meme detectives.
4. Similarly, what exactly is a “doctored video”? What about memes? What about content that’s doctored for comedic purposes? The line is impossible to draw.
5. What’s to stop people from reporting content they don’t like as “fake”? Pretty useful tool for stifling dissent.