Mastodon is unusable if you follow Lemmy communities, so no one does.
But that wasn’t my question. If a Lemmy instance I am on federates with Threads, how do I find people on Threads, follow them, and have their posts appear in my Lemmy feed? The people who are saying it can be done are not also explaining how it can be done. You seem to be saying, in a roundabout way, that it cannot be done?