Maybe I’m missing a basic concept on Federation. I was assuming that the federation feature would allow a user on another instance (e.g., on Baraza.africa) to post on Lemmy.ml.

Here are two posts that Baraza.Africa shows as being posted to c/bitcoin: https://baraza.africa/c/bitcoin@lemmy.ml

However, on !bitcoin@lemmy.ml, those posts do not show. https://lemmy.ml/c/bitcoin/data_type/Post/sort/New/page/1

Is that correct, expected behavior?

I am seeing the same. It seems that Mastodon cannot follow a Lemmy commmunity if a user on that Lemmy instance has the same name as the community.

I created issue #1922 for lemmy on Github for this.