I can't guarantee a fix, but see:
Why is my Apple ID setting greyed out on iPad? https://discussions.apple.com/thread/8355468.
A post in this thread says: "I just found the reason for my Apple ID Settings being greyed out. When I disabled Restrictions, my Settings became enabled and I was asked to update Apple ID Settings. S O L V E D...
Apple ID banner grayed out https://discussions.apple.com/thread/8611970. This one reports a solution also having to do with restrictions.
My Apple ID is Greyed Out in Settings, Fix https://macreports.com/my-apple-id-is-greyed-out-in-settings-fix/
This occurs “most likely … because of a problem that happened when upgrading the iOS or when you change your Apple ID and password.”
So, you might use What to do after you change your Apple ID or password https://support.apple.com/en-us/HT204071
To get Apple Support for help with your problem, see:
Apple ID Support https://support.apple.com/apple-id
Apple Support Twitter https://twitter.com/AppleSupport There might be an hour or so wait.
Apple ID account security for country-specific andregion-specific help https://support.apple.com/en-us/HT204169
Get Support: We’re here to help https://getsupport.apple.com/. Go through the options to find the best support option for you.
