IMO, where lemmy is right now. Niche communities are counter productive. Especially as there is often 3 times the same niche communities on 3 different instances.
Try to talk about your niche content in a larger community. Talk about Oshi no ko in a generic manga/anime community. Try to talk about Kult RPG in a generic rpg community. Talk about french politics in a general France/Europe community.
Today we have generic community with like 10 posts a day and under them a bunch of niches with a post per week. Uf you move these posts to the general community above you now get 15 posts a day.
Content is what drags users, not yet another niche community.
Lemmy is still on the verge of usability, there is few very engaged user who make a large fraction of the content. Keeping it alive, but if in 6 month they have less time some /c will deperish