Use Blender to import .FBX 3D files, and export them to .usdz to use in Apple Motion.
Many 3D models are available in the .FBX Autodesk's format. Unfortunately Apple Motion only accepts .usdz files.
It's easy to use Blender as a converter:
- In Blender, File, Import, FBX (.fbx)
- The model will load in Blender with its Materials/Textures.
- Then File, Export, Universal Scene Description (.usd*)
- In the filename export, use ".usdz" extension. In the export settings, under Materials, Select "512" in the USDZ Texture Downsampling.
- Export USD.
The resulting .usdz file imports fine into Motion with its Materials/Textures attached.
Thanks to this Lightcraft documentation for the tip.