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.
bluesky will eventually enshitify like reddit and twitter did and like all social media platforms with investors/financiers behind them always do. (reddit in particular promised not to enshitify at the beginning just like bluesky is promising right now).
be ready to find a new social platform like you had to do with reddit in another 4 to 9 years if you go with bluesky.