There are a lot of small, informal and fuzzy communities around specific interests in Twitter. For example, I routinely run into the same folks talking about some specific areas in PL/FP or in complex systems/resilience engineering. These sub-communities aren't clearly delineated like a subreddit, rather they arise organically through the same set of people following each other or, at least, consistently appearing in each others' feeds and conversations.

Utaite. Will find barely any anywhere else. Thankfully if you're in one of those sub-communities, you don't ever get recommended anything political or American.

It seems like most of Japan.

Discord is my goto choice for communities now, but I fear that company is not on a great trajectory either. It's like voting, you're picking for the least evil

Nazis, groypers, Christian Nationalists