I am a big NFL fan, and I found the instance nfl.community. It has a community for each team, as well as a general NFL community. I joined a couple of the communities through my lemmy.world account, but it sees no posts there. I know this instance isn't defederated from nfl.community, so why wouldn't I be able to see any posts? I don't understand, what am I missing?

EDIT: I just reread my post and realized that I didn't mention that there are tons of post on all the communities on this instance, but nothing shows when logged in through World.

SOLVED: So I had the chance today to reread through this thread and do some digging based on the replies, and I've figured out the issue. I went back and looked at nfl.communities, and it turns out that can@sh.itjust.works is correct - all the posts on that server are by users that are from the alien.top instance. Those aren't actual users, alien.top just scrapes posts & comments from Reddit. So those aren't actual posts by Lemmy users, and, as can said, there wouldn't be any engagement from anyone on that server, because they won't see my posts & comments. Lastly, I followed a link can posted with bot rules, and one of lemmy.world's policies is "Bots shall not just be posting Reddit content", which is exactly what alien.top is doing. That explains why World is blocking all the posts from the nfl.communites server.

Thanks to everyone who responded and helped sort this out!