Looks like you should be able to copy/paste the URL of the community in your Masto search bar, such as https://beehaw.org/c/politics, but this seems to only work with the Beehaw technology community (https://beehaw.org/c/technology). A nondescript 500 server error is returned when I try any others. Is this expected? Is there some kind of toggle for each community that allows/disallows following from other Federated instances?
~~My guess is that those are Mastodon accounts created with the same name as the link to the community. Someone correct me if I’m wrong. That would explain why the others aren’t showing up as they haven’t created Mastodon accounts. ~~
After further research I’m totally wrong.