Is Firefox Private Network available in iOS
According to the webpage:


  This extension is currently available to US desktop users only.


This means that it is only available for desktop Firefox.

However, the extension is allegedly based on the same infrastructure as CloudFlare's Warp VPN service, which is currently being rolled out to the "1.1.1.1" app if you have it installed.

The Warp VPN appears to be available on iOS and in all countries.