Use Screen Time to set an app limit
Open Settings
Tap Screen Time
Tap App Limits
Tap Add Limit
Select the app category or specific app
Tap Next
Set the time limit to 1 minute
Turn on Block at End of Limit
Tap Add
Use Guided Access to lock the phone to one app
Open Settings
Tap Accessibility
Tap Guided Access
Turn on Guided Access
Set a passcode
Open the app you want to lock
Triple-click the side button
Tap Start
Use Face ID, Touch ID, or a passcode to lock the app with Screen Time restrictions
Use a third-party app lock feature if supported by the app
Use Shortcuts automation to restrict access to an app-related action
Hide the app from Home Screen and App Library if needed