Microsoft is already working on Windows 10 version 21H2. This has started with build 21264. The update will bring an updated user interface to the OS, with a number of major features.
Microsoft is planning a big Windows 10 update in the second half of 2021 that will introduce new top-level features and a new user interface which is more modern and consistent. There will be a focus on wider adoption of WinUI in the Windows Shell and native applications, an updated taskbar built with modern code and an improved user interface for the old File Explorer.
The user interface changes are now known as 'Sun Valley'.
Microsoft will still issue two feature updates in 2021 as per the biannual update scheme. However, the significance of the updates will be reversed. The Spring update, version 21H1, will be a smaller service pack-like update, similar to what we have already seen in Windows 10 20H2 and 1909. The bigger one with more notable changes, 21H2, will come in the second half of 2021.
Windows 10 21H1 (minor update) will be released early next year followed by the major Windows 10 21H2 in the fall. Windows Insiders can already test Windows 10 21H1 update, but in addition to this, the company is also working to launch preview builds of the 21H2 update.
According to the source, Microsoft has already started testing the 21H2 branch with Windows 10 Build 21264. There are no public releases of version 21H2, it is being tested internally (via WindowsLatest).
Also, check out: