The App Store App cannot be deleted from the iPad. Perhaps you have moved the App Store App to an App Folder? Try searching for the App using the native search tool; just swipe downwards on any empty of a Home Screen to expose the Search dialogue, then search for App Store.
If your iPad has iPadOS15.x installed, it is possible to delete the App icon (but not the App itself) from the Home Screens; if deleted from your Home Screens, it will still appear in the App Library:
Use the App Library and Home Screen to organize your iPad apps - Apple Support
If you are unable to add or remove Apps on your iPad, you might need to check your ScreenTime restrictions:
- Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > Adding Apps - ensure that this permission is set to Allow
- Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > Deleting Apps - ensure that this permission is set to Allow
Lastly, if still unresolved, perform a forced-restart of your iPad - as this will often clear an isolated software issue:
- On an iPad with a Home button:Â Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
- On other iPad models:Â Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.