There should be a universal community search engine for the Fediverse where you type in a community description or keyword and the service returns a list of all similar communities across all of the instances. It should be called Feddle (the Fediverse Google.)
Are you talking about this: https://lemmyverse.net/communities ?
There’s this one too: https://browse.feddit.de/ but it is not as nice.
Yes, thank you.