Not very surprising to lose users after the big intake from June. If that were the only intake we'd ever get I would be worried but we all know that Reddit will continue to do user-hostile things. Lemmy now exists as a permanent lifeboat for those who get fed up with Reddit over time, and the next time something big happens we'll be better prepared.
We need more "subs" like wallstreetbets, ama, LPT... I'd engage more if there were more comunities I were interested in and they regularily showed up on my feed
These will probably need to grow naturally again. We have enough techy users to carry tech-related discussions, but we probably don't have enough users to carry niche communities yet. By gaining more users of any kind, techy or otherwise, we have better odds of gaining people with a secondary interest in those niche communities. It'll take some time, but the Fediverse is much more permanent, and investments here will pay off theoretically forever. Even if another open platform supersedes Lemmy, it will be easy to port our community over to it.
I feel like for subs like those to pop up, the barrier to entry needs to drop really low. We lean even more technical than reddit did now, and to encourage subs like those, you kinda need a healthy population of non-technical people.