The app will always display a sign which will indicate to the users that they need to unlock the app using the fingerprint authentication.
There is a significant new update rolled out by in its Android beta app to version 2.19.83, as traces of a new Authentication feature could not be identified. These setting changes were in the pipeline for a very long time now, and if the latest update is anything to go by, there has been a lot of progress made already. Beta tracker WABetaInfo has shared screenshots which reveal exactly how the Authentication feature can be enabled in Settings, and how the interface will appear for that. This will not immediately start working for the beat users as the feature, as of now, is disabled by default.
As per the tracker, this particular Authentication feature will allow WhatsApp users to lock their account, and then unlock it using a fingerprint sensor. It can be enabled in Settings; Account; Privacy; Use Fingerprint to Unlock. WhatsApp will register the fingerprint as soon as it is enabled. There will then be an option which will then ask if the user wants the app to be locked immediately (after you leave the app)/ after 1 minute/ after 10 minutes/ or after 30 minutes.
The app will always display a sign which will indicate to the users that they need to unlock the app using the fingerprint authentication. Also, an error sign will pop up if the app is not unlocked even after multiple tries.
This feature has not yet been rolled out, but it will be in use for beta users in the next set of updates. It needs to be mentioned here that iPhone users do already have this aforementioned feature in the stable version of the iOS app. Apart from fingerprint authentication via Touch ID, facial recognition via Face ID is also available to iOS users.
WhatsApp is also working on Dark Mode, as was evident when it was spotted in one of the recent beta updates. However, there is no official word on when this mode will actually be a part of the stable version.