Spam has consistently been the death of the open internet, even the big tech silos struggle with spam (Instagram for example -- despite having incredibly invasive techniques for identifying "genuine" users -- is STILL inundated with spam commenters). I think instances on the fediverse should reconsider their open registration policy, either totally close registrations when you reach an agreed upon critical mass of users, or adopt some form of invitation or application system for new users. I believe Mastodon supports both in the software.
Speaking from experience, they could fix their spam and abuse woes very easily by just closing new signups or restricting it in some way. Simplest would be invite-only (built-in feature of Mastodon), or restrict the signups page based on IP range whitelist/blacklist.
EDIT: Their domain has been reinstated, and they disabled open signups. New registrations now require moderator approval https://pawoo.net/@pawoo_support/111249170584706318