Its always a good idea to secure access to you mobile devices with fingerprint and facial recognition scanners – and if your device will allow it, you can use the same security features to to secure access to your apps.
Now it’s possible for Apple iOS users to set their WhatsApp account to require Face ID or Touch ID authentication when opening WhatsApp, even when your device is already unlocked.
You can still reply to messages from notifications & answer voice / video calls if WhatsApp is locked. It’s also possible to set the duration of time before the Screen Lock will start.
Settings > Account > Privacy > Screen Lock > Toggle on Require Face ID / Require Touch ID > Select the time duration (Immediately, after a minute, after 15 minutes or after an hour).