And the culling of Windows features continues.
Windows Mixed Reality is deprecated and will be removed in a future release of Windows. This deprecation includes the Mixed Reality Portal app, and Windows Mixed Reality for SteamVR and Steam VR Beta.↫ Microsoft’s “Deprecated features for Windows client” page
All this mixed reality stuff was a big push in Windows, up to the point Microsoft added applications and dedicated folders for it to Windows. I don’t think I’ve ever seen anyone use any of it. The Verge notes Microsoft has been downsizing its VR efforts for a while now, and it seems the company is bailing on the VR hypetrain.