Download a few that I created https://thedigitallifestyle.com/w/index.php/2018/06/25/here-are-some-custom-windows-mixed-reality-environments-for-you-to-download/

I have written about how easy it is to create your own Windows Mixed Reality environments just using Microsoft’ Paint 3D app, so I thought I would make a video show just how simple it is.
In this video I show how you can create your own space, populate it with objects and how to get the scaling right just using Paint 3D. You do not need any special tools or training to get started just a Windows Mixed Reality headset, Paint 3D and some imagination.