Windows 10 21H1 is the next feature update to be released and delivered as an enablement package that enables dormant features already installed on Windows 10 2004 and Windows 20 20H2. Microsoft began testing the Windows 10 feature update (build 19043) in February after releasing it on the Windows Insider ‘Beta’ channel. Microsoft has been releasing new cumulative updates to fix bugs and newly discovered security vulnerabilities. The more exciting features are expected in the fall with the release of Windows 1021H2, the Sun Valley update.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-moves-windows-10-21h1-to-the-release-preview-channel/