I feel having a balance between more popular and widely used communitys as well as smaller and nicher ones work pretty well for me, where I admin 3 rather popular and broad communitys and 3 small and very niche ones. That way it just feels like more is happening yknow?
I also can only recommend utilising a Post Schedueler and making 1-2 weeks worth of posts at a time!
When you manually post daily, it does feel pretty lonely, but if you do all the work in a few hours for 2 weeks like I usually do, it really does feel less like shouting into a void since you aren't actively posting per say that way