The error is telling you that you dont have the required extension (which are in babylon.manager.js)
If you wanna use the raw geometry only in a project without babylon.manager.js then you need to select these options:
- Primitives instead of sub meshes
- Right handed instead of left handed
- And disable Unity Metadata
Note: You will only get RAW GEOMETRY including any materials and animations… Nothing else that babylon.manager.js provides like shadows, lightmaps, reflection probes, script components, etc…