The idea that you might want Lemmy and Mastodon to work well together is honestly kind of silly to me.
They are structured and built from the ground up to be entirely different kinds of social platforms. Mastodon is structured around people publishing their thoughts. Fundamentally it’s simply a kind of blog network. Lemmy is structured around topics and conversation. It’s essentially a forum network. I can’t see a way they could blend seamlessly, forget if they should. (They shouldn’t)