> Is freecad and blender usable?

Blender works in VR (using any OpenXR compatible headset). To view scenes in VR, you can use the free built-in VR Scene Inspector addon. To edit and create scenes in VR, you can use the Freebird XR addon for Blender (https://freebirdxr.com/).

Fingers crossed for OpenXR working properly in Steam Frame! In which case Blender and other OpenXR-compatible apps will work too.

Disclaimer: I'm the author of Freebird XR, a VR editing addon for Blender.