Windows 10 build 21387 (co release)

Windows 10 build 21387 (co_release) is the nineteenth Insider Preview build of Cobalt, the 21H2 development semester of Windows as a service. This build was released on 21 May 2021 to all Windows Insiders on the Dev Channel.

Changes

 * Internet Explorer 11's functionality has been disabled and attempting to run its executable file will open Edge instead. It is still possible to run Internet Explorer if   is replaced with a copy from an older build.
 * The "Eco mode" experimental Task Manager feature introduced in build 21364 has been removed.
 * The first log-in has been updated to use smaller and Segoe UI Variable text, though the flashing animation is still kept.

News and interests

 * The flyout might occasionally flash in the screen's top left corner when opened.

Camera Settings

 * The Camera app does not respect the brightness adjustments made to a camera under its respective page.

Installation

 * The update process to this build has a chance of hanging for extended periods of time.
 * Some devices might fail to upgrade to this build with error code  due to a second issue different from that in build 21382.

OOBE

 * The OOBE may use an incorrect font when this build is ran under Simplified Chinese language pack.

General

 * Certain parts of Search, including the File Explorer search box, are not displaying correctly in the dark theme.
 * The icons for Microsoft Edge and File Explorer in the taskbar are swapped in clean installations.