The notice is for the "Apple Store" app and that is not the same thing as the "App Store" app. The Apple Store app can be used to buy Apple hardware while the App Store app is used to download apps (software).
You can open the App Store app and download the Apple Store app from it.
If the App Store app is missing from your device, see the following.
The App Store app is not one of the apps that can be deleted but with iOS 14 on an iPhone it can be removed from the home screen. If you have iOS 14 on an iPhone, go to the App Library (swipe left past your last home screen). From there you can touch and hold an app and slide it left back to the home screen.
Another reason for it not being visible is due to a restriction on purchasing. Go to Settings and tap Screen Time. tap Content & Privacy Restrictions. tap iTunes & App Store Purchases. choose a setting and set to Allow. See: https://support.apple.com/en-us/HT201304#prevent-purchases
If that is not the cause, try using Search to see if that will locate it: https://support.apple.com/en-us/HT201285