But Linux is not a platform in general. It is already next to impossible to write software that requires “Linux” and nothing more with all the kernel functiona

But Linux is not a platform in general. It is already next to impossible to write software that requires “Linux” and nothing more with all the kernel functionality that can be enabled or disabled. Linux is a component of many different platforms, which indeed do provide different libcs, but also different t.l.s. libraries, different c.p.u. architectures, different Linux configurations and whatever else. As far as I know with respect to Windows, it only provides stable interfaces viā C libraries, and does not have a stable binary interface to the kernel directly.