I searched Lemmy in the app store. I didn’t (and still don’t) understand why there are a bunch of third-party apps that connect to Lemmy. But it seemed like Voyager was popular, so I went with that.
There were many third party Reddit apps before Reddit had their official app. And you could argue that Jerboa is the official Lemmy app since it is made by one of the main Lemmy devs.
Lemmy is not one centralized entity or corporation, so it is impossible for a first party app to exist. Think of it like a collection of separately run clubs/groups that all communicate with each other over the same medium. But the medium is not run by a single person or company.
However, Jerboa is the app made by Lemmy devs themselves, so I suppose it's as close to "first party" as you can get.
Totally fair, and there are actually some official or "first party" apps of parts of the fediverse, like the Mastodon app, which is (or at least was) somewhat subpar when compared to third party offerings, but I believe was put out mainly to give new users a starting point.