Back in November 2021, we learned that WhatsApp is working on a new desktop app available via the Microsoft Store. Reports at that time claimed that the app is based on Universal Windows Platform (UWP) instead of Electron and also packs inking and multi-device support. Now, it appears that the development team is moving to WinUI 2.6 and newer to take advantage of the Fluent Design elements in Windows 11.
This discovery was made by Windows leakster FireCube (@FireCubeStudios on Twitter), who noted the differences between the new and old versions of the WhatsApp Beta app:
We enrolled in the WhatsApp Beta app as well to have a look and a Windows 11 makeover is definitely in the works. You'll notice rounded radio buttons, drop-downs, and more elements that are in line with the Windows 11 design language. That said, it is definitely a work in progress and there are still some UI elements that are inconsistent with Windows 11, but that is the nature of a beta so it's understandable.
You can download the WhatsApp Beta from the Microsoft Store yourself to give it a go. It works on both Windows 10 and Windows 11, but you will need to enroll in the beta for multi-device support in order to proceed. The instructions are mentioned inside the app which you can download from here.