Windows 10 build 20239

Windows 10 build 20239 is an unleaked build of Iron. Two screenshots of this build were posted to GitHub by a Microsoft employee on 21 October 2020. It was also mentioned in a Feedback Hub quest about the Memory Diagnostics Tool: "If you get the error: “Your computer has a memory problem” then:
 * Contact your OEM for support if you have system problems. To increase stability, on Windows Insider builds 20239+ the bad pages will be avoided until a future scan."