you can go to an instance and hit local and see which communities are local to that instance https://lemmy.world/communities?listingType=Local

or you can just browse all communities with https://browse.feddit.de/ then hit the copy button and search it in the instance you are signed in to, sometimes you have to hit the search button a few times for it to show up, and you might have to hit the subscribe button a few times too so it doesnt say pending and says joined instead

I made a tool for that just yesterday: https://directory.fstab.sh/. Or try https://lemmyverse.net/ for something much more fancier.