Swipe down on the Home Screen and use Spotlight Search to find the app
Check the App Library by swiping left past all Home Screen pages
If the app is in a hidden Home Screen page, long-press the Home Screen, tap Edit, tap Edit Pages, then select the hidden page and tap Done
If the app is in a folder, open the folder and drag the app back to the Home Screen
If the app was removed from the Home Screen, open the App Library, press and hold the app, then tap Add to Home Screen
If the app is hidden by Screen Time, go to Settings, tap Screen Time, tap Content & Privacy Restrictions, then allow the app
If the app is restricted by age settings, go to Settings, tap Screen Time, tap Content & Privacy Restrictions, then adjust app restrictions
If the app is hidden in Purchased apps, open the App Store, tap your profile, tap Purchased, then download it again
If the app is offloaded, go to Settings, tap General, tap iPhone Storage, then reinstall the app
If the app is still missing, restart the iPhone and check again