This was also complained about in this post: https://www.androidauthority.com/reddit-alternatives-lemmy-3335429/ and probably mirrors experiences of other lemmy-users, especailly new-comers.

One paragraph reads: “Sure, there are categorization tools like Lemmy map that let you look up instances, but the Matrix-like grid will certainly not make things any easier for the average user. Even after logging into Lemmyworld, it took me a while to figure out that the local tab restricts all conversations to discussions on the Lemmyworld server. Switching the tab to all and catching up on discussions happening in the broader multiverse of Reddit alternatives is also possible. Still, there’s no visual identifier that guides you toward it.”

This was also my first impression of Lemmy and why I almost dropped it: I thought I could only interact with the communities on my server, which was very frustrating until I saw the filter for “all” and that I could join them just like that. Then it was fine.