How to use private Wi-Fi ?

Howto get over the weak security if Wi-Fi ?

Check the router settings, see the following Apple articles:

Recommended settings for Wi-Fi routers and access points

Recommended settings for Wi-Fi routers and access points - Apple Support

• About privacy and security warnings

If your Apple device shows a privacy warning or weak-security warning about a Wi-Fi network, that network could expose information about your device. Apple recommends connecting to Wi-Fi networks that meet or exceed the security standards in this article.

How to use private Wi-Fi ?

Do you mean use Private Wi-Fi addresses?

If so, see -> Use private Wi-Fi addresses on iPhone, iPad, iPod touch, and Apple Watch

Use private Wi-Fi addresses on iPhone, iPad, iPod touch, and Apple Watch - Apple Support

If you use Private Wi-Fi addresses then you can assign the iPhone a MAC address & a Private IP address.

Log in to the router, add your iPhone NAME + iPhone MAC address  + private IP address.

Your iPhone MAC address is: go to Settings -> General -> About -> the Wi-Fi address (note this address).

Assign a private IP address to the iPhone, for example 192.168.x.xxx or 169.254.x.xxx. 

This depends on the router & other iDevices that have already been added.

What is important, check the list and the last xxx must be different from the iDevices that have already been added.