Can you list the wikis you say are "closed"?

Personal wikis are allowed as long as everybody is allowed to edit.

Public Editing
Communities are about working together, and all Fandom communities are  open to the public to edit. There is no option to restrict editing to  the founder or to a particular group.

@Oot42 Thank you!

No, personal wikis are not allowed. You can create a test wiki if you need one (but only one) but other wikis need to have a clear topic. They can't just be "stuff me and my friends like/made up" - even if you let anyone edit.

@Sannse

"No, personal wikis are not allowed."

Perhaps Fandom should change the very first sentence shown when creating a new wiki then:

Also, I think I remember seeing other staff members here saying that wikis for personal projects are allowed, but private wikis are not.

Guess it depends on the individual definition of the term "personal", as this seems not to be very clearly definied.

Yes, I agree it's not defined well. But a valid topic is one that is based around a distinct topic that other people can edit. It can be very personal in the sense of being a passion project that isn't going to build into a massive wiki, but it's not personal in the sense of "me and my mates messing round with a wiki about us and our stuff".

I've made a note to define this better in the future