A lot of the anime-related communities have consolidated over time to the ani.social instance. There are historical reasons for this (largely due to hostility from the ml admins), and if you want a brief history for just the general anime community, I previously wrote a post here.

That being said, the ani.social instance has been growing with new communities being added. Here are the more active ones:

General Communities

• !anime@ani.social
• !manga@ani.social
• !lightnovels@ani.social

Series-Specific Communities

• !dungeonmeshi@ani.social - Delicious in Dungeon community
• !frieren@ani.social - Frieren: Beyond Journey’s End community
• !nokotan@ani.social - My Deer Friend Nokotan community (currently airing show)
• !dandadan@ani.social - Dan Da Dan community (show airs this fall)
• !dragonball@ani.social - Dragonball community

Misc.

• !vocaloid@ani.social - Very new community just started by @hisao@ani.social about vocaloids. Check it out!
• !vtubervids@ani.social - Community to discuss and share videos from and about vtubers
• !seiyuu@ani.social - Community about Japanese voice actors behind the scenes

A couple fandom communities:

• !nokotan@ani.social - Currently airing show, has weekly discussion threads
• !dandadan@ani.social - Show that will be airing this fall, has threads for manga chapters
• !frieren@ani.social - Show that aired a couple months back, currently mostly fanart posts
• !dungeonmeshi@ani.social - Show that aired a couple months ago, currently mostly fanart posts
• !seiyuu@ani.social - Community to discuss Japanese anime voice actors behind the scenes and share clips

Thank you!

The project relies on extensions that are installed separately to pull content from different services (mangadex, mangaplus, etc.). The other day, the tachiyomi devs removed almost all the extensions that they were hosting/maintaining after a threat of legal action from a Korean webtoon company. Here is a relevant discussion thread.

Here is a guide to a third party extensions repo that was linked in a discussion thread the other day.

I haven’t personally done this with my Tachiyomi yet, but have heard from others it has worked well.