What ive been doing is going to each server on lemmy via their joinlemmy page that lists all the servers and then opening the list for their local communities. I then just type it out in the url bar and subscribe, one community at a time.
Tedious, but i'm also new and I'm not finding another way to both discover it exists and subscribe to something i want to follow. I know that I can search for it via @ community @server.whatever but without knowing what names to use and which servers to find them on, its functionally worthless. But again, i'm just a recent reddit refugee so I probably dont know all the shortcuts