I can’t sign out cause of the restriction

The person that has enabled the restrictions in ScreenTime, needs to disable them.

If you have forgotten the password for ScreenTime, check this article:

If you forgot your Screen Time passcode - Apple Support

If an app or feature on your device is not working or is restricted, it may have been disabled using Screen Time by you, 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