You can always try to filter these kinds of posts in the meantime? Or even have your own database of filtered spam related usernames? See https://discuss.flarum.org/d/5131-filter-filter-posts-with-keywords.
Spambots are getting smarter as the years fly by, I believe the best approach is to filter titles, posts, and keep a database listing of our own of crowd sourced spambot usernames/emails (Akismet solves this but it isn't really full-proof most of the time). There hasn't been a perfect solution yet due to spambots becoming smarter at bypassing spam prevention systems.
Though, there is one way that this can actually be tackled. An extension that basically displays your forum rules along with a tick-able checkbox which says that you agree to these rules when posting for the first time. It can also have a timer that can be set to allow for a wait time before ticking said checkbox. Spambots are very "automatic" and programmable so it's gotten easier to study their logic and patterns. Though, there are times where spambots are actually real people, yet rare to see, I did get cussed out by a few in my time by calling them filthy ?
