"sign out is not available due to restrictions"
If an app or feature on your device is not working, it may have been disabled using Screen Time, or by an IT administrator if you are using a device owned by an employer or educational institution. See how to use Screen Time on an iPhone, iPad, or iPod touch by clicking here --> Use Screen Time on your iPhone, iPad, or iPod touch - Apple Support
Related information about how to use parental controls on your child's iPhone, iPad, and iPod touch to restrict access to features --> Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support