@CathyBikesBook
https://blacktwitter.io/about is an instance that is what it says.

blackqueer.life is as well, it uses allowlist-only federation to make a safer space for members. I'd guess they don't federate with mastodon.social due to poor moderation. https://blackqueer.life/@tillshadeisgone/113312617711895513

Depending on your interests you could apply for accounts there, I'm sure the local timelines are great places for discovery. The local timeline of blacktwitter.io is also public so you could look there for accounts to follow.