Safari Extensions for iOS - where is it?

According to https://developer.apple.com/safari/extensions/ I can "Enhance and customize the web browsing experience on Mac, iPhone, and iPad with Safari Extensions".

Sounds great so far.

I am looking for information on how I can can create a Safari Extension on iOS, and I have come up blank.

All the docs make no mention of iOS, just MacOS.

The sample code at https://developer.apple.com/documentation/safariservices/safari_web_extensions/messaging_a_web_extension_s_native_app?language=objc is for MacOS only.

Xcode project templates list "Safari Extension App", but only under MacOS.

I'm lost, are WebExtentions / Safari Extensions supported on iOS, and if so, how?

There are apps in the iPhone App Store that claim to integrate with Safari. What technology are they using?