Windows 10X build 19561

Windows 10X build 19561 is an unleaked build of Windows 10X. This build is mentioned in three screenshots on Microsoft Docs in the article about the Microsoft Emulator, along with builds 19531 and 19540. Judging by the dates provided, it could have been compiled on or before 7 February 2020.

Source
Use the Microsoft Emulator - Microsoft Docs