On version 0.19 you can block instances so that you don’t see any posts from that instance, instead of having to block communities one by one, you still see comments from users of that instance in other posts so it isn’t completely blocking the instance.
Blocking the instance does not stop Threads comments from being displayed on any federated instance.
Even if a user blocks Threads, they will still be exposed to misinformation and hateful, extremist comments/users.