testing free stuff on PC, VR headset and mobile: YouTube
Certainly none of it is carefully designed as mobile-first, but it does work mobile out-of-the-box on even on mobile. Collision detection is rather heavy though, and it does show.
VR headset view required most work, pointer selection predicate had to be carefully crafted, but that was all.
All models are open source, published on Sketchfab by their authors under CC license, auto-converted to GLTF. Minimal intervention required, like a texture here and a plane there.