https://wccftech.com/builds-from-windows-10-manganese-20h2-to-drop-soon-for-insiders/

Microsoft today delivered a Preview Build from Windows 10 20H1 - which it has decided to assign version 2004 despite its early release - to both the Fast and Slow rings. In the release notes, the Windows maker warns those in the Fast ring to switch to the Slow ring if they want to stick to the stable builds of Windows 10 20H1.

The company said that it will soon start "releasing new builds" from its development branch, which usually delivers super early and often unstable builds to those in the Fast and Skip Ahead rings (which has closed for the season). Windows 10 20H1 has apparently moved out of this development branch aka RS_PRERELEASE to the VB_RELEASE branch.