It's called scrolling and/or blocking communities.
The fact that you saw a post and immediately said "I can't deal with this! Get it out of my sight!" but didn't bother to see the solution literally at your finger tips...
Just ignore posts you don't like. If you can't deal with posts you don't like being in your feed, stop browsing All. There are so many solutions to this that don't involve completely dog piling onto people (and other communities) that did not (and don't) post the content you didn't like.
Join an instance that's defederated is your only real option. Even if you could block the instance you can't block all the users, which is why most of the replies to your post are from hexbear users trolling.
Not sure why your admin decided to not defed despite the toxicity and hate they showed to him.
some clients i think have that functionality (not rightly sure which), and i know it is a planned feature for lemmy as a whole eventually, but honestly if you saw one bad post, just downvote and move on, leave a comment on it expressing your distaste, or just block the user, or the community, right? i feel like wanting to block a whole huge instance over one stupid post seems a bit over the top tbh.