I want to make someone a Content Moderator on the wiki I'm the admin on (celebrity.fandom.com), but it seems like I'm not allowed to do anything apart from making them a Discussions or Chat Moderator. Why can't I do this, and how can I go about making them a Content Moderator if the option to do that is greyed out on the user rights management page?
You have put in your adoption request. Merrystar was set (11 years ago, yesterday) to complete the adoption, but almost 20 minutes after she posted "you're all set" on the (OLD old old Style!!) request, Scarecroe was assisting her and promoted you to Admin (but not 'crat).
You'll need to Adoption:Requests to ask for Bureaucrat rights. Be sure to add that to the "more info" section.
I'm pretty sure that wiki must have a very high amount of audiences also since *before* you can even adopt that wiki (which if you had a high audiences level they must edit on the wiki and you yourself before adopting the wiki itself you MUST create a blog post for a weak but audiences must sign and think about it if you can even adopt it.) which is one of the adoption rules and plus if you don't even have that many audiences you might end up getting fandom closing down your wiki which sadly many people got wikis shutted down in the process by admins....
Good luck then according to the rules from the wiki adoption article here