Back when Microsoft acquired Hotmail, a horde of software specialists were tasked with porting this platform to Windows. After burning the one or other fortune on this project, they finally gave up. Hotmail kept running on Linux until they killed it.
Microsoft’s been pretty open about using Linux for at least the past decade or so.
They kept building it into Windows which eventually resulted in WSL, largely because they use Linux servers but Windows workstations.
It was about 5 years ago that they publicly released Common Base Linux Mariner (now called Azure Linux).
Back when Microsoft acquired Hotmail, a horde of software specialists were tasked with porting this platform to Windows. After burning the one or other fortune on this project, they finally gave up. Hotmail kept running on Linux until they killed it.