From the article: Moving to the Fediverse This tension between these communities and their host have, again, fueled more interest in the Fediverse as a decentralized refuge. A social network built on an open protocol can afford some host-agnosticism, and allow communities to persist even if individual hosts fail or start to abuse their power. Unfortunately, discussions of Reddit-like fediverse services Lemmy and Kbin on Reddit were colored by paranoia after the company banned users and subreddits related to these projects (reportedly due to “spam”). While these accounts and subreddits have been reinstated, the potential for censorship around such projects has made a Reddit exodus feel more urgently necessary, as we saw last fall when Twitter cracked down on discussions of its Fediverse-alternative, Mastodon.
Kinda. You’re server will not back-populate old posts from someone you just followed. However, you should get all future posts.
If you find a thread on Lemmy and you want to comment on it in Mastodon, but you can’t find it normally, you can copy the URL to the thread or comment, paste it in Mastodon search, and then it should force-load that post. Then you can reply and comment on it as normal.