https://www.bleepingcomputer.com/news/microsoft/windows-10-insider-preview-build-18329-released-with-mixed-reality-win32-apps/

Microsoft has released Windows 10 Insider Preview Build 18329 (19H1) to insiders in the Fast ring. This build adds top apps in Search, desktop Win32 apps in Windows Mixed Reality, and Mail & Calendar version 16.0.11231.20082.