After following setting up WSUS for Windows 10 20H2 upgrade, the workstation updates actually failed with an error code 0xc1900223.
The error code reveals nothing. Nothing useful in the event viewer either. But the log from WSUS does.
(Unable to Find Resource ) ReportingEvent. Client 181: Parameters: Feature update to Windows 10 (consumer editions), version 20H2, en-us x64
More specifically, the message “unable to find resource” indicates that the workstation can’t find and download the upgrade package from the WSUS server. Since the update package has an extension name .esd that is a supported MIME type on IIS server out of the box, adding the extension name should fix the whole thing.
Go to the server that runs WSUS service, open IIS manager, and select the server name on the left and open the MIME type on the right.
Click Add and add the following type to the server.
File name extension: .esd
MIME type: application/octet-stream
Now back to the workstations that failed the updates earlier and give another try. This time, Windows 10 20H2 upgrade should go through fine with no more errors.