How exactly would that work? Or, perhaps more specifically, how would the app know whats anime and whats not? muting and blocking the communities yourself would be far easier IMO.

You’ve gotta block the communities yourself. I feel your pain, but what you’re requesting isn’t going to happen.

Every time I come across an anime community, I block it. But there are so many that keep popping up…

My block list is filled with so many anime, furry, and shitposting communities. It’s a bit annoying and an uphill battle, but you’ve got to go to their communities and block them individually (but also block the anime instances).