Today, Microsoft is releasing Windows 10 Insider Preview build 20211, the newest preview from the development branch, to the Dev channel. As usual, there's not a whole lot that's new. In fact, there are two key new features in this build.
One is that there is search on the Default Apps page in Settings now, so you can just go and search for a file extension to find it. The other is that you can access Linux file systems in WSL. Here's the full changelog:
Adding Search to the Default Apps pages in Settings
After making some updates to help improve performance, this change to enable searching the lists of file types, protocols, and apps when setting a default is now rolling out to all Insiders in the Dev Channel – thanks everyone who’s shared feedback along the way.
Access Linux file systems in the Windows Subsystem for Linux
This latest insiders preview build adds the ability for users to attach and mount a physical disk inside of a WSL 2 distro. This enables you to access file systems that aren’t natively supported by Windows (such as ext4). So if you’re dual booting with Windows and Linux, and are using different disks, you can now access your Linux files from Windows! To learn more about this feature please read this blog post on the Windows Command Line blog.
Keep in mind that being that this build is for the Dev channel, it's not tied to a specific feature update. These features could arrive in 21H1, is 21H1 even happens, they could arrive in a later update, or they could be canceled completely. This is the nature of perpetually taking builds from the rs_prerelease branch.
As always, you can grab the build from Windows update. If you're not on the Dev channel yet, you can sign up through the Windows Insider Program tab.