So for a long time Iv been wanting to write custom overlays in openxr and with the help of Claud I have managed to actual achive it.
So here is the repo Mattlekim/MonoXR: A OpenXR overlay implementation. Using monogame as the renderer.
Using monogame code you can now write custom overlays in openxr. Now this runs headless No game to run the updates and draw.
there is basically an overlay that is your screen space, you can set that wherever you want in 3d space. You can specify the width, height, and depth from the HDM, Along with other things.
Then you have a RendertargetOverlay
Here you can use spritebatch, load textures, text or just draw polygons and the render target will get sent to the overlay.
Each RenderTargetOverlay has its own independent Pos, Size etc
Hopeful its of some use to others.