Restrictions on iPhone
Child phone not allowing to sign out of Apple ID due to restrictions.
Question marked as
If an app or feature on your device is not working or is restricted, 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. Read this document about using Screen Time on an iPhone, iPad, or iPod touch --> Use Screen Time on your iPhone, iPad, or iPod touch - Apple Support
Tap Settings > Screen Time > Content & Privacy > scroll to Allow Changes.