Ok - I just figured it out but it was not intuitive. This is for kbin.social. Unsure of the differences to Lemmy.
You have to go to search, then click magazines. This link should take you right there:
Then search for what you want eg newcommunities.
That should show local communities as well as ones that are federated.
It wasn’t apparent on mobile but apparently there’s a subscribe button on the search results on the right side.
If you click on the community you can still subscribe but clicking the side bar on the left. There’s a subscribe button if you scroll down a bit.
I don’t think memmy works with kbin.social yet.