On Mastodon, Friendica, Pixelfed and if I'm not mistaken also Bookwyrm you can verify yourself by using your own website (if you have one). You can also do it for free if you have an account on a bunch of services such as Gravatar.I haven't seen anything like this on Lemmy fwiw.

I mean to also be fair here, that's not a unique feature of the Fediverse. We currently have some drama (in Germany) about people impersonating people on X. The commercial platforms even earn money doing the same thing. And it's very clear in the prelude to a potential court case, they have no intention to stop this. They're currently doing some really weird shenanigans so the lawyers can't serve any papers or mail.

Not sure how it is on other platforms. It's been a while since I helped people to get rid of unwanted content on social media. But it was never easy. And once you do it for privacy reasons or mild doxxing, you're basically screwed. Because these days they'll all make you pull down your pants to prove it's legitimate. So you basically end up doxxing yourself to protect your private information. I mean what's more likely to happen is, they don't even listen. But I'm not really up to date with that any more. Maybe they changed and now they do? But I doubt it. It's just how the internet operates.