Haven’t seen much about this project nor if it will be open-source. But it looks at least promising and I really loved Apollo in the past.
I think any good alternative client that can use the current momentum of kbin/lemmy is good.
Even more since Jerboa is afaik developed by one of the two main devs of lemmy and they will probably/hopefully focus more on the core development and I doubt that they can maintain an additional mobile app at the same time.
Unfortunately there isn’t an ideal solution for this. You will only see communities that at least user of your instance has subscribed to.
Posts in those communities will show up in your ‘All’ feed.
For all others is the best way an external community browser like this one:
https://lemmyverse.net/communities