there is a user (Jellende2065) spamming THOUSANDS of low quallity things every single day i made an account for the first time in years specifically just to block this user and its not working

users are impervious (i.e. taking no damage like a cheating SoulsBorne ultra-secret boss) to the blacklist..the best option is to move on,and find a better way to dig through this place.

edit: on second thought....gelbooru's currently hiring volunteer mods,and you can be a part of it

gelbooru.com/index.php?page=forum&s=view&id=8369

If I recall it's not really a block feature but you can add that users name to the blacklist and you won't be able to see that person's uploads

Not a complete solution, but if you add -user:Jellende2065 to any search it'll hide all of that user's uploads from that search's results. Use the saved search function to have your most common searches with -user:Jellende2065 and you'll avoid seeing a lot of their uploads.