Hey Florent,
You seem to have made the Datasmith connection to your Archicad scene which is great. Now all you need to do is be on the 3D view inside of Archicad and press the Sync button on the Datasmith toolbar, or turn on Auto-Sync, then click back into your Twinmotion scene and that geometry should come through.
You can reference the full workflow here:
- https://twinmotionhelp.epicgames.com/s/article/Getting-Started-using-Datasmith-Workflows-with-Twinmotion?language=en_US
Thanks,