There’s no clear alternative, but we have a few that could take off if a lot of people gave them a try. The first one that comes to mind is Mastodon. Even Jack Dorsey says Twitter can never be what we need. We need a standard protocol like email, not a centralized service that can be controlled by any single entity. Mastodon could fit that. It’s what you call “federated”, like email. You have independent servers that use the standard Mastodon protocol. It’s not super hard to setup your own server and once you do your server’s users can talk to users on any other server that hasn’t explicitly blocked yours.