Maybe I am not understanding the fedivers well enough, but why am I not seeing communities like !flippanarchy@lemmy.dbzer0.com from my europe.pub account?
The instances seem to be federated.
Edit: they are accessible when using a direct link like the one in the first paragraph, but the search function doesn’t seem to work.
I think that it only federates new posts after someone subscribes as well, so when viewed on your instance it may not have as many posts as the community’s instance.