Now you can use biometric security on your phone to protect access to WhatsApp's iOS app. Depending on your iPhone model, you can use Face ID or Touch ID to restrict access to the software. This feature, first discovered by 9to5Mac is available in WhatsApp version 2.19.20 and can be activated from the Application Privacy menu in Account Settings.
Although it is not possible to secure a message by chat, the new biometric security layer needs to keep the content of the message more secure, even if the mobile device itself is already locked. . If you select App security settings, be aware of the notification settings (especially message previews). If enabled, you can view and reply to all messages without unlocking the app. You can also answer WhatsApp calls without first unlocking the app.
This feature is currently only available for iOS versions of the app, but recent testing by WABetaInfo last month shows that the Android launch is in progress.