Swipe down on the Home Screen and use Spotlight Search
Check the App Library by swiping left past the last Home Screen page
Open the App Store and tap your profile icon, then tap Purchased
Go to Settings, then Screen Time, then Content & Privacy Restrictions
Check Settings, then Home Screen, to see if apps are set to App Library only
Open Settings, then Siri & Search, and make sure the app is allowed to appear in search
Check if the app is hidden inside a folder on the Home Screen
Go to Settings, then General, then iPhone Storage, and look for the app
If the app was removed, reinstall it from the App Store
Restart the iPhone if the app still does not appear