As reported by WABetaInfo, WhatsApp for Android Beta v2.19.221 allows users to try out the fingerprint lock feature before the feature makes its way to the stable release channel. Screen lock is available for users on the abovementioned Beta release, and who are using it on Android Marshmallow and above. Of course, you also need to have a fingerprint sensor on your phone to use this feature. You can find the feature nesting under WhatsApp Settings > Account > Privacy > Fingerprint Lock.
You can choose to hide content in notifications too, once fingerprint unlock is enabled. WhatsApp also lets you choose from the locking interval, though the time interval options available feel a bit restrictive; we’re sure the service will consider more options in the future. Also, note that the widget content is hidden by default when you enable the feature, though if you wanted privacy in your chats, you wouldn’t be adding a preview widget to your homescreen. WhatsApp is also reportedly making use of Android’s fingerprint APIs, so your fingerprint data is only used on-device for authentication and not sent to Facebook’s servers.
To try out this feature, you need to have WhatsApp for Android Beta v2.19.221, which you can sideload through APKMirror. If the feature is not enabled for you, you can try backing up your chat history and reinstalling WhatsApp. We tried to enable the same but were unsuccessful, so perhaps your luck shines better. If not, you can always wait for the feature to be made available in the Stable release.