I use a lemmy client for android called Jerboa. There is an official community on lemmy.ml dedicated to news about its development, but on jeremmy.ml I can’t find it and subscribe to it.

Hi, That’s because the developer of Jerboa is also one of the developers of Lemmy platform and co-admin of lemmy.ml instance (@dessalines@lemmy.ml). So the official channels about the Lemmy/Jerboa development are in that instance. On the other hand this community is related to technical topics of this instance [jeremmy] only.

Is there some sort of whitelist here?

See: Instances

Or I don’t fully understand how Lemmy works?

See: Docs