February 27, 2020—KB4535996 (OS Builds 18362.693 and 18363.693)
https://support.microsoft.com/en-us/help/4535996/windows-10-update-kb4535996
Highlights
Updates an issue that prevents the speech platform application from opening for several minutes in a high noise environment.
Updates an issue that reduces the image quality in the Windows Mixed Reality (WMR) home environment.
Updates an issue that might prevent ActiveX content from loading.
Improves the battery performance during Modern Standby mode.
Updates an issue that causes Microsoft Narrator to stop working when a user session is longer than 30 minutes.
Addresses an issue that adds an unwanted keyboard layout as the default after an upgrade even if you have already removed it.
Updates an issue that prevents the Windows Search box from rendering properly.
Updates an issue that prevents the printer settings user interface from displaying properly.
Updates an issue that prevents some applications from printing to network printers.
For other Improvements and fixes please refer to Support Article linked above.
February 27, 2020-KB4537572 Cumulative Update for .NET Framework 3.5 and 4.8 for Windows 10 Version 1903 and Windows Server 1903 RTM and Windows 10, version 1909 and Windows Server, version 1909
https://support.microsoft.com/en-us/help/4537572/kb4537572-cumulative-update-for-net-framework
For Quality and reliability improvements please refer to Support Article linked above.
Edit: For further information on Optional Updates refer to post of Sumit - Insider MVP in this thread.
Edit 2.0: Additional update for Windows Defender.
KB4052623 Update for Windows Defender antimalware platform
https://support.microsoft.com/en-us/help/4052623/update-for-windows-defender-antimalware-platform
This package includes monthly updates and fixes to the Windows Defender antimalware platform that is used by Windows Defender Antivirus in Windows 10.
Monthly updates are installed in addition to major Windows 10 releases. Both types of updates should be installed to ensure continued protection against malware and other threats.
~bhringer