Support for this in core Lemmy has been discussed many times. There's an open issue for it that's been gathering dust for a while. Some apps already implement this on the client side I think, not jerboa though.

This would need to be added to the lemmy backend first.

This would be nice, even if the content is not there yet

My use case for this is that I only subscribe to communities related to tech to keep my core feed clean. Specially during short breaks during work hours I don't want to open Jerboa and bump into other stuff. But I have other interests, like most people.

So it would be nice to have a feed of communities focused on politics even though I'm not subscribed to those communities. And another one focused on random interests like documentaries, books, etc (which I'm not subscribed to either).

I believe this should be part of the back end though, and not a frontend-only thing, in order to have sync between clients (like smartphone, tablet, PC). Having to redo lists in each frontend would be a pain when lists can have many dozens of entries. (During the dark ages of reddit I remember hitting the 100 limit at some point.)

Yes. Click on the three lines in the upper left for the menu then click on "subscribed"