PSA: fandom.com runs a honeypot to trap wiki admins who try to leave Fandom.

As mentioned in this article, you can submit a "request" to Fandom to close your wiki.

If you submit such a request, Fandom will not close your wiki. Instead, they will
a)Remove your admin status to prevent you from deleting articles,
b)Keep a close eye on your wiki to make sure you aren't trying to migrate away from Fandom,
c)Possibly ban your account from Fandom.

There are ways to essentially trick Fandom's automated system into closing your wiki. All such methods are against the rules of Fandom and rely on your wiki avoiding the notice of any human employees of Fandom.

If you want to know how I got them to close Pandora's Tale Wiki, DM me, either here or on Matrix. I don't want to post the explanation publicly in case Fandom notices and changes their system to prevent my method from working for future wikis.