PR4100 New Share/USB How To Set Default Behaviour as Private?

PR4100 Firmware version 2.31.195

Adding new share created with public access as default.
Creating new user is creating default share with public access.
Attaching usb flashdisk/external hdd created share with public access as default.

This make my storage vulnerable dangerous to be accessed by other users before i turned off public access by manual.

How to make this default behaviour as private?

Usb content availability has been turned off but it doesnt worked. References: [ASK] USB Content Availability in Cloud Access & Full Access of USB Drive attached