I wasn’t familiar with Fedilab but I’m pretty sure that it’s just a way to see and interact with instances you’ve already joined. I think where you’re getting confused is, you don’t join “The Fediverse” with one instance, they may not communicate well yet. I’m not sure if there are issues with choosing an instance on Lemmy (with the reddit style that might make it confusing) with Pixelfed (where it’s all pictures) and Mastodon (where it’s microblogging). Also, Lemm.ee might be defederated or not able to communicate with all the places you want to go. I would try different types of instances and maybe another instance on lemmy to see if that works. Growing pains.