Blocking doesn't do anything to stop the spread like on Mastodon or Reddit, best to report and reach out to admins (reports can be dismissed by moderators sometimes). Lemmy's blocking as it is, is only useful for Communities (soon instances) you want to keep out of your feed and for snowflakes who 'don't wike what person say'. Seriously the ability to restrict malicous users is a very important feature for both user and community safety.