First, you gotta set a parental controls passcode and turn on Content and Privacy Restrictions.
To set a passcode, tapUse Screen Time Passcodeand enter a four-digit code when prompted.
To set restrictions, tapContent & Privacy Restrictions.
Enter the passcode, then turnontheContent & Privacy Restrictions.
Each of these configs sets whether or not access is locked behind the passcode.
Turn a setting on for maximum security.
Other Screen Time controls
The mainScreen Timemenu has a few more restriction options:
