Can't find the files app

The Files app is a built in app in iPads running iOS 11 or later. While it can be deleted, it can also be reinstalled from the App Store.

Why exactly can't you download it from the App Store?

Link-> https://apps.apple.com/us/app/files/id1232058109

What happens when you open that link?

If it has an "Open" button, it means its already installed on your iPad. It may be removed from your home screens, or placed inside a folder. You can use the App Library to try to find it: link-> Find your apps in App Library on iPad - Apple Support

If it has a cloud icon, then you can tap on it to download and install it. Link-> Redownload apps and games from Apple - Apple Support

For an iPad with iOS11 or later, if not already installed on your iPad, the Apple Files App can be installed from the App Store.

https://apps.apple.com/gb/app/files/id1232058109