@Xoart, @MoodDreamButterfly
In case if you're still looking for it, you need to update Vive Business Streaming on your PC to beta and through it on your headset too. After that, there'll be a new experimental feature in the graphics settings. Enable it and set the camera rendering in your Unity camera to solid color, set it black with alpha = 0, the passwthrough will render instead of skybox. It will also render on any object where material's alpha is <1, note that