https://www.bleepingcomputer.com/news/microsoft/windows-10-kb5003214-cumulative-update-preview-released/

Microsoft has released the optional KB5003214 Preview cumulative update for Windows 10 2004, Windows 10 20H2, and Windows 10 21H1.

This cumulative update is part of Microsoft's May 2021 monthly "C" update, allowing users to preview the upcoming updates and fixes scheduled for the forthcoming June 2021 Patch Tuesday.