kbin (kbin.social is currently working) allows individuals to block by domain. That would keep any top level memes off your /all but I think you still see comments.
I'm not sure that's actually a thing. Maybe he means individual magazines / communities, which have a little block button next to the subscribe button in the sidebar.
"For example, you want to block lemmygrad.ml - go to kbin.social/d/lemmygrad.ml (d for "domain") and from there you can block the whole instance (click on the 🚫)."