All they really have to do is specify that all new machines sold domestically have to be loaded with their tailored Linux distro and no other OS, and they’d eventually get rid of the majority of Windows machines. Enforcement of that should at least be possible, since they’d only have to check sellers and distributors of new equipment. Then just lean on domestic developers and/or software companies so that they don’t provide new versions of must-have applications (whatever those may be) for Windows to encourage the holdouts to move on. It would never fly in a country without an authoritarian government, but China could likely get away with it. It just wouldn’t be instantaneous.