arPlacement property
Selects whether to place the object on the floor (horizontal surface) or a wall (vertical surface) in AR. The back (negative Z) of the object's bounding box will be placed against the wall and the shadow will be put on this surface as well. Note that the different AR modes handle the placement UX differently.
You may use the ArPlacement enum to set this attribute.
<model-viewer> official document: https://modelviewer.dev/docs/#entrydocs-augmentedreality-attributes-arPlacement
Implementation
final ArPlacement? arPlacement;