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!