Users will be able to lock an app when they hand over their phone to do things like show someone a picture or let them play a game. When an app is locked, if someone tries to tap the phone, they will be required to authenticate using Face ID, Touch ID or a passcode.
While the app lock feature is enabled, information from inside the app won’t appear in other places, like search and notifications. Users can also hide an app that they don’t want others to know is installed. The hidden apps appear in a hidden, locked folder.
Guided Access locks you into a single app.
This hides and prevents opening specific apps, the rest of the phone is still accessible. It’s much more convenient as something you would configure and keep on all the time.
This article does not describe the feature well. It prompts to open, not when trying to exit.