Welcome! You’re going to want this to find communities on different instances. Not only will this show you communities that aren’t available on your home instance (either because no one’s requested it yet, or you aren’t federated with them), but it will also show you when the same community name exists on multiple instances.

https://lemmyverse.net/communities

Also:

https://RedditMigration.com

https://sub.rehab

https://github.com/maltfield/awesome-lemmy-instances