Just a heads up, since I was having some trouble at first:
1 - Go to communities > search 2 - If you search for a given community and it doesn’t shows up, it looks like it is not indexed yet 3 - Search for the community in this format !community (Like !foss) 4 - After that, I had to go back to step 1 and simply searching for ‘foss’ returned what I wanted. But looks like the page needed to be updated.
Also, this tool might interest you guys. It is a universal community search in Lemmy instances: