My App store app is not on my Iphone 12pro

check Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > Installing Apps

make sure that's set to 'Allow'

Or if you have no checked the App Library already.. check there..

From your Home Screen, swipe left until you get to the App Library.

Swipe downward and you'll get an alphabetical list of your apps.

Locate the app in the list or type the app name into the search field

Once you've located the app, tap/hold until it raises/selects, then drag it and it'll pop out to your Home Screen

Organize the Home Screen and App Library on your iPhone - Apple Support