Windows 10 build 21343.1000

Windows 10 build 21343.1000 is the twelfth Insider Preview build of Cobalt, the 21H2 development semester of Windows as a service. This build was released on 24 March 2021 to all Windows Insiders on the Dev Channel.

Iconography improvements
Many icons in  and   have been updated to follow the Fluent Design system. As a result, those used in user folders, drives, ribbon items, and other areas in File Explorer, including Run, have been refreshed. Some Control Panel applets have also seen their icons revamped, including the app's default shell icon.

Other changes

 * A new runtime that is designed and optimized for container scenarios has been introduced, which allows faster launch times for Windows Sandbox and Microsoft Defender Application Guard (MDAG).
 * The Windows Administrative Tools folder in the Start menu has been renamed to "Windows Tools".
 * The News and interests flyout is now available in the Chinese market.
 * The new IME candidate window design introduced in build 21313 is now available for the Simplified Chinese IME.
 * The "Get help" link in the touch keyboard's settings has been renamed to "Learn more".
 * Network-related surfaces across Windows now use the updated icons introduced in build 21327.
 * File Explorer has been updated when renaming files to support using Control + Left/Right to move the text cursor between words in the file name, as well as Control + Delete and Control + Backspace to delete words at a time.
 * The issue where on some high-refresh rate monitors, games will be limited to 60Hz while users with variable-refresh-rate monitors may experience tearing issues, has been fixed in this build.

Bugs

 * The update process to this build has a chance of hanging for extended periods of time.
 * The option to discard changes in custom caption styles is not working in this build.
 * Upgrading to this build will cause Quick Access in File Explorer to reset itself to default configuration. To keep pinned files and folders, backup all files in  before upgrading and restore those to the aforementioned path after upgrading.
 * Some games will not work in this build or cannot synchronize saved data when a game is played on a different device or will not save data when a new game is installed.
 * In some display scalings, certain system folders with redesigned custom icons might just use the default one.
 * Search may crash on launch.