Not that I know of ... but there should be IMO! I've said so previously elsewhere.
It might be a lot of work, but it'd be something that only a good app/client could possibly deliver, and IMO, probably move the needle on what people think of what the fediverse can be.
If any developers are reading this ... I'd say give it a shot! There are probably plenty of open source apps you could copy from!
The UI is peobably the main problem, I imagine. The app would need to know how to portray a certain post - in the Lemmy style or in the Mastodon style?
Yeah, it seems like being able to follow people is a feature for Lemmy that will arrive at some point as it opens up the Fediverse more but the developers probably have more pressing matters and implementing it might be tricky (I believe kbin is a bit clunky in this regard).