Hot and Active sorting kind of suck right now tbh. Try top>day or something.
Edit to elaborate: I believe active heavily weighs recent comments and it sort of creates a feedback loop where someone comments, putting the post to top of active, then others see it there and comment on it perpetuating the cycle.
The website now let's you sort top 12h, 6h, and 1h too but no apps seem to have that implemented yet.
Oh and sort by All not Local to see communities from other instances that users on your instance have subscribed to.
Check lemmyverse.net too to look for communities no ones subscribed to where you are yet.