At one point, I recall being able to at least search for a Mastodon user from Lemmy and have them come up in search results (no posts and couldn’t follow).

Hmm, I think that still works provided the Mastodon user has interacted with Lemmy in some way. It will pull up their bio and posts/comments made on Lemmy, but that’s it.

I think the difficulty lies in the way the two platforms treat user accounts. On Mastodon, it’s pretty straightforward - a user is a user.

On Lemmy, the users are users, and the community federates to Mastodon as a “group” that boosts/retweets every single post and comment that users make to that community. It’s not really ideal, but I’m not sure if it can be improved considering the radically different structure of each platform. This is what the Quark’s feed looks like on Mastodon: