How can I deactivate private browser on Ipad

While you can't permanently disable the feature, you can use Parental Controls on your child's device:

Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

I don't think you can "deactivate" that option. You can just turn it on or off, as per the steps provided in the support article that led you here.

If you'd like, please submit your request to Apple directly, using this link:--> Apple – Product Feedback

Thanks and regards

Giulio