https://www.bleepingcomputer.com/news/microsoft/microsoft-releases-windows-10-ssu-to-fix-security-update-issue/

​Microsoft has released the Windows 10 1909 KB5000850 cumulative update preview and a new KB5001205 Servicing Stack Update that resolves a Secure Boot vulnerability.

The KB5001205 Servicing Stack Update (SSU) will automatically be installed by Windows Update to improve the update experience. This SSU should not be skipped as it fixes an issue installing a previously released Secure Boot security update.