The first batch of security updates or ‘B’ updates are now available for all supported versions of Windows 10 including version 20H2. The cumulative update comes with security fixes and general bug fixes, and the patch is rolling out to PCs with May 2020 Update, November 2019 Update, May 2019 Update and later. Users of the Microsoft Input Method Editor for Japanese or Chinese languages might experience issues when attempting various tasks. Devices using Windows Update for Business or that connect directly to Windows Update are not impacted.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-cumulative-updates-kb4586786-and-kb4586781-released/