it's not about whether your platform is open or not, but about who's making the devices and what you're forcing them to do.
XBox is only made by Microsoft, there are no XBox OEMs, and Microsoft can do whatever they like to their devices. They're not forcing any manufacturer to do anything, because they are the manufacturer. Same with iPhones, Play Station consoles and so on.
Windows computers and Android phones are manufactured by many companies, and Microsoft and Google were engaging in anticompetitive behavior by forcing everybody who wanted their OSes to do certain things, and that's the problem here.
XBox is only made by Microsoft, there are no XBox OEMs, and Microsoft can do whatever they like to their devices. They're not forcing any manufacturer to do anything, because they are the manufacturer. Same with iPhones, Play Station consoles and so on.
Windows computers and Android phones are manufactured by many companies, and Microsoft and Google were engaging in anticompetitive behavior by forcing everybody who wanted their OSes to do certain things, and that's the problem here.