I always think of small communities id like to be a part of, but can never find any. Reddit had (has) the same issue, leading people to create subreddits around the idea of helping others find communities to fit their interests. Idk thought it would be cool but I don’t have the capabilities to do it myself.
There’s [email protected], [email protected] and [email protected].
Also Lemmyverse which can search and list communities from across the threadiverse.