Windows 10 build 18946

Windows 10 build 18946 is a private build of Windows 10 May 2020 Update. This build was not intended to be released but accidentally flighted to all insiders in the Fast Ring on 24 July 2019. It is currently the only leaked build of the  branch.

Breaking the known insider releases routine, Microsoft managed to also release 18947.rs_prerelease as well as 18947.rs_xbox before pulling all three releases after publishing the AMD64 variant of this build within five minutes.

They also broke the UX routine and showed up with some new major changes.

New features
Both features can be enabled using mach2.
 * Fully redesigned Start menu. It is likely intended to be used in the upcoming Windows 10X operating system. It currently works properly only with the Light theme.
 * New Control Center and Notification Center design. Now it's more compact and convenient. By default it only shows buttons, but it expands as you receive notifications.