Use lemmyverse.net
Click the home icon and set your home instance and then search for whatever you want. All links will open in your home instance and you can then just subscribe.
I’m probably missing something easy, but where do you “just subscribe?”
There are a few communities that show up in lemmyverse, but aren’t showing up when I search in my app (Jerboa)
Open the link from lemmyverse in a browser tab and click Subscribe. If on mobile you might have to expand the sidebar first. Then go back to Jerboa.