Isn't that just the 'communities' list in the hamburger menu? Or if you mean browsing the posts, browsing by 'all'? Unless maybe I misunderstood your question...
As far as I can tell that only shows communities on my own instance, or all communities everywhere. What I'm looking for is a way to browse communities on a different specific instance.
To give an example, I was browsing all posts and saw a post from french instance jlai.lu. I was hoping there was a way to find a list of all their communities somehow.