Be sure you're running at least the Windows Update (1903), which is the minimum requirement for Windows Mixed Reality end users to run OpenXR applications.To start developing OpenXR applications for immersive Windows Mixed Reality headsets: Getting started with OpenXR for Windows Mixed Reality headsets If you're using the emulator, the emulator image will reset each time you start it, and so your best bet is to just make sure that you have the latest version of the HoloLens 2 emulator image.
