Windows 8.1 build 9477 (fbl partner out21)

Windows 8.1 build 9477 (fbl_partner_out21) is an unconfirmed build of Windows 8.1. This build is a later compile of build 9477. It is known that this build exists only in the ARM architecture. Two photos was found on the Chinese website BetaWorld. It was supposedly uploaded to the aforementioned site on 4 May 2019, but at the moment this cannot be confirmed or refuted as it is not publicly available.

According to BetaWorld Wiki, found on two Lumia 2020 engineering machines, one of which has a blue screen error message on boot, and the other one can enter the system normally but crashes quickly. In fact, although out21 was compiled later than out31, this Build was first used for the image production of Lumia 2020.

The watermark style is different from out31. According to the lab, it is tentatively estimated to be M2 Build, and more evidence is needed.

Bugs
Some core files are damaged, and only the recovery environment can start normally.