Hmm, only Mastodon is mentioned for this feature in the ActivutyPub spec... I'm not sure if it's the only service that has implemented this fully or if it's just the example used.

https://swicg.github.io/activitypub-data-portability/#move-action

That's ashame, because account mobility is the most important tool for healthy decentralization. The reason Facebook or Twitter can "get away with" implementing such shitty policies and abusing their users is because the users are locked in, with a high cost to switching platforms.

The cost is highest for accounts like small businesses that live and die by social media marketing, once they have an established presence and successfully built a following on a platform, it is very risky for them to give that up and start over on a new one.