where can i find User Guide for iPad Air 4th Gen

iPad Users Guide iPadOS 14.4.

Tap the link below

https://books.apple.com/us/book/ipad-user-guide/id1515995498

The Apple version is called the "iPad User Guide"

It is obtained through the Books App.

After starting App, select "Book Store" and search for iPad User Guide, the latest version cover iPadOS 14.4.

There is not a specific guide for the iPad hardware, it is generally covered through the iPadOS

There are other non Apple guides that can be found in the Books App for a price.