WhatsApp tests Material Design tweaks on Android to make it look more like its iOS app
The navigation bar will replace the current tabbed interface that sits at the top of the chat list. This gives users the option to access Chats, Communities, Status, and Calls from the bottom by cycling through a more clearly labeled navigation system accentuated by its corresponding icons.

Current WhatsApp UI on Android | Source - Phone Arena
The bottom navigation bar switches between a dark and white color scheme, depending on your theme choice. This is the same navigation bar that is used on the iOS version of WhatsApp, and it is more in line with Google's design guidelines for Android apps.

Light vs Dark Bottom Nav Bar | Source - Wabetainfo
The new bottom navigation bar is currently being tested with a limited number of users, but it is expected to be rolled out to everyone eventually. The change is likely to be welcomed by users who prefer a more simplified interface, and it will also make it easier to use WhatsApp with one hand.In addition to the new bottom navigation bar, WhatsApp has also been rolling out Material Design tweaks such as redesigned switches and floating action buttons with rounded menus. It is unclear when these changes will be rolled out to everyone, as they are currently available in beta and to a limited amount of users, but they are all part of WhatsApp's efforts to improve the app's user experience.ncG1vNJzZmivp6x7sbTOp5yaqpWjrm%2BvzqZmp52nqHy4tMCtqpqooGKxpr%2FIoKVmrKearqy%2FjKilZpmemb%2BwtcNmo6inm2K6sL7EZqOio5VitrC%2FvqKbamxoaH51