Just right after i wrote about this type of spam on Reddit - reference https://lemmynsfw.com/comment/281912
see 2nd and 3rd posts in screenshot
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https://join-lemmy.org/docs/users/04-moderation.html
from the documentation there is a way to ban a user from the site, but only admins have access to it, might be worth trying to coordinate with them to ban them
This is definitely something that will require bots.