Microsoft is losing Builders fast. They’re switching to MacOS and Linux. The biggest pull keeping people on Windows, outside of shear inertia, is content creation and gaming. However, even these are falling to Linux.
Without Builders, you don’t have software, and without software, you don’t have users. This is why Microsoft needs Windows Lite.
I think mono may still exist somewhat, but .NET Core took it as a foundation and built on top of it in the best way possible. I do hobby dev with .NET on Linux but sadly still beholden by Windows for work for the time being.