your instance has a list of communities federated to it here: https://piefed.zip/communities

the most active community for announcing new communities is !newcommunities@lemmy.world (which includes communities on many different instances, not only .world)

This can help https://lemmyverse.net/communities

!lemmy411@lemmy.ca would be best for that. You can also ask in the various c/nostupidquestions communities

!communitypromo@lemmy.ca might be what you're looking for.

https://lemmy.ml/c/findacommunity

its not very active but it exists

I just use the features within voyager app. Can see every community by various sorting or searching

https://piefed.social/topics is fun to look through.