To get a sense of how that would work, check out #InteroperableFacebook, a video and essay I put together with @eff to act as a kind of #DesignFiction, in the form of a user manual for a federated, interoperable Facebook:

https://www.eff.org/interoperablefacebook

He points out that this kind of mandatory interop is a preferable alternative to the unconstitutional (and unworkable!) speech bans proposed by #Florida and #texas
37/

An #InteroperableFacebook would make it easy to leave social media by removing the penalties Facebook imposes on its disloyal users, and the EU's privacy framework means that when they flee to a smaller safe haven, they won't have to worry about commercial surveillance:

https://www.eff.org/interoperablefacebook

26/