Web and App VR on iPhone 12 don't work

Hi,
On iPhone 12:

  • With the Sketchfab app, I load a model. I click on the VR icon. The app then prompt me to insert my phone in a VR headset. After a few seconds, the 3d model is displayed in normal mode, not in VR mode (same behavior on Android LG G6) .

  • In Safari, the model is displayed in VR mode, but the distance between left and right view is too wide (probably because of the size of the screen), resulting in the VR view not being well displayed in the VR headset

  • In Chrome, the browser is well displayed the view in VR (the view is like in Safari too wide), but it is not following the movement of my head. On my LG G6, the view is perfect but I can’t move.

Any clue how to view a model in VR on iPhone12?
Thanks