I think you'd find Pleroma interesting, it has old Twitter vibes but Mastodon is way fuller by far. But it's interoperable with any Fediverse platfotm, this is an invite-only instance ran by one of the devs post.ebin.club, other two but public ones:
They are already here 😊. I use Mastodon and don't mind that more people come over. It's an interesting, active and friendly network with noticeable growth.
But I guess Bluesky has it's own positive vibe and is an equally good choice for now.