I think most popular apps (boost, voyager if i remember, etc.) have this feature. I dont believe lemmy has this natively.
Note that blocking instances doesn’t mean you wont see comments from there. It only works on communities.
To be honest though, most of the problematic people only comment on specific posts/communities so blocking certain keywords and instances should fare pretty well.
The pole is to prevent people from taking carts and similar objects up and potentially causing an accident
Though it does have unintended consequences