How to add 3D Overlay for SteamVR

I am trying to use the OpenVR Overlay API to overlay a 3d model on top of another VR application.

I have successfully used this API using this HeadlessOverlayToolkit to overlay plans.

I arranged 6 planes to make a 3d cube and overlay it.

I am trying to figure out that there is a way to overlay real 3d models, and if so, how?

I see in the OpenVR docs , it says it IVROverlay

allows displaying 2d content via composer. However, of course, if it is possible to build 3d shapes (using 2d planes), then why not overlay 3d models?

Any insight, experience, or guidance here would be appreciated.

All the best

Liam