It doesn't show up in my instance either. Sometimes it takes a little bit, but I also noticed lemmit.online has an older version of Lemmy, so not sure if that can make a difference
I just realized that entire instance is just a bot crossposting posts from reddit via a bot. I got excited looking at the post count, but didn't realize that the actual user engagement is next to nothing. So, I don't want to subscribe after all!
Another point, I think with the way federation happens, searching from your instance doesn't always work. I might be wrong, but I believe going directly to /c(or m)/community@instance and subscribing will actually link things up for searching.
That only that only works sometimes, unfortunately. About half the time when I go directly to a community from an instance I'm not on, my only option is to sign up with an account, not to subscribe with my current account from my home instance.