WhatsApp messenger upgrades its Security features on the iOS app to add a Screen Lock feature. The app access the Face ID or Touch ID feature on your phone when it’s time for the app to lock.
How to enable the features
Go to settings on your iPhone to Account Privacy and enable the Screen Lock.
The new features work on old iPhones without Face ID by using the Touch ID, on the newer iPhones, you make use of the Face ID Screen Lock method.
The major function of this update on iOS app involves the ability to lock your app behind your authentication system, nobody have access to your WhatsApp till you unlock the app yourself.
Locking a selected chat is not working yet, but locking the whole app behind your authentication system is a very good feature. Download & Enjoy the new WhatsApp on the Apple Store.