How do I turn permanently disable or remove private browsing from Safari so my teen does not search unwanted web content?
Mac Pro
You don't have the ability to permanently disable Safari's Private Browsing. Simply do not use it.
If your teen has his own user account on your Mac and it's not an administrative account you can try setting Parental Controls in that account and see if Private Browsing is one of the items you can control. You can certainly block certain sites or types of sites.
Set up parental controls on Mac - Apple Support
Check which apps and websites your child has used on Mac - Apple Support
How to disable private browsing on Safari
