Microsoft releases a new Windows 10 build for the Windows Insiders who are on the Dev Channel. The latest Windows 10 build 20211 contains two new features. Among these, one is the ability to search for default apps, and the other is the ability to access the Linux file systems in WSL (Windows Subsystem for Linux).
If you are a Windows Insider and your device is enrolled against the Dev Channel, you can grab the latest preview build through Windows Update. Before upgrading to this build, make sure to check out the original release notes for known issues present in this build.