Hello,
It appears you cannot find your App Store app. This issue is mentioned in this support article --> Download apps and games on your iPhone or iPad - Apple Support
Certain built-in apps cannot be deleted so it is somewhere on your device. It can be hidden* by you, or by an administrator if your device is managed by an education or business institution. In the latter case you need to contact the administrator.
See if you hid it with restrictions:
It appears you have already checked Screen Time.
See if it is in your App Library -->
Organize the Home Screen and App Library on your iPhone [iOS14] - Organize the Home Screen and App Library on your iPhone - Apple Support
"Search for it ( Use Spotlight Search on your iPhone, iPad, or iPod touch - Apple Support ). Swipe down from the middle of any home screen and type the name of the app into the search field at the top of the screen. If it is in a folder, it will show the folder on the right of the app name after you tap on the app when it appears in the search."
"Reset the Home screen layout which will return the [app] to the home screen as long as it isn’t restricted. When you do this, it returns the home screen to out of the box condition and it will destroy any folders you had on the home screen. Settings > General > Reset > Reset Home screen layout."
* Use parental controls on your child's iPhone and iPad - Apple Support "If you turn off an app or feature, the app or feature won't be deleted, it's just temporarily hidden from your Home Screen."
If none of those work, contact Apple. Refer to this page for Apple Support features ➔ Contact - Official Apple Support
Select from the presented options until you find a solution for your issue, or see if there is a chat or phone call contact method offered lower on the page (you sometimes have to narrow down the options multiple times before this is shown). If you do not see your issue, keep experimenting with any series of selections until you reach one that offers a chat session or a telephone call and get the representative to redirect you.
This support article has various country telephone numbers for contacting Apple for support and service ➔ Contact Apple for support and service - Apple Support