https://wccftech.com/required-security-update-released-for-all-versions-of-windows-10/

Microsoft has started rolling out an extended out-of-band update to several versions of Windows 10, including the May 2019 Update, version 1903. While multiple updates have become a norm for Windows 10, today’s release also carries a note from the Windows maker where the company says that this update is a required security update that “expands the out-of-band update dated September 23, 2019.”

Microsoft added that today’s security update includes a mitigation for an Internet Explorer vulnerability and a fix for a printing issue that was reported after the release of the last cumulative update. The company advises users to install the latest update ASAP and restart their devices for the mitigations to take effect.