Does iCloud Drive need to be enabled in order to determine whether someone is signed into iCloud? Because it seems like it does, which I don't recall reading anywhere before.
With iCloud Drive disabled, a call to CKContainer.default().accountStatus() returns status: CKAccountStatus.noAccount, error: nil
With iCloud Drive enabled, the same call returns status: CKAccountStatus.available, error: nil.
I had a user report that syncing wasn't working, and it turned out that she had disabled iCloud Drive, not knowing what it was or whether it benefited her.