Apple ID is greyed out i

Have you checked Settings/Screen Time for any restrictions?

Some other things you can try. Do you have access to another WiFi network where you can try? That has worked for several people.

Try a restart.

Restart your iPhone, iPad, or iPod touch         

Try a forced restart.

Reset Device.      

If necessary

Hard reset.        

If there are restrictions in Screen Time that are preventing access, you will need to restore the device to factory settings. Do not restore from a backup made when the Screen Time code was active.

If there aren't any Screen Time restrictions, do a backup and try a factory reset. Then restore from your backup.

Restore to Factory setting.      

Backup - Restore your device from an iCloud or iTunes backup.     

Maybe this will help. 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 similar solution 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/