Swipe down on the Home Screen and search for App Store
Check all Home Screen pages and folders
Open App Library and look for App Store
Go to Settings
Tap Screen Time
Tap Content & Privacy Restrictions
Tap iTunes & App Store Purchases
Tap Installing Apps
Set it to Allow
Go back to Screen Time
Tap Content & Privacy Restrictions
Turn Content & Privacy Restrictions off if needed
Go to Settings
Tap General
Tap Transfer or Reset iPhone
Tap Reset
Tap Reset Home Screen Layout
Check for App Store again
Go to Settings
Tap General
Tap Software Update
Update iPhone if available
Restart iPhone
If App Store is still missing, sign out of Apple ID and sign back in
If needed, contact Apple Support