>>>>some good information in this thread concerning "export layout" in AutoCAD
This thread is about export layout method, but:
1/ There is no EXPORTLAYOUT command in AC for Mac.
2/ Seems OP needs 3D model, but when you export layout to model, you will get 2D view of 3D model.

To export full 3D model from Fusion to AutoCAD, one have to export Fusion model as a STEP or IGES file, then import to AutpCAD, but again - AutoCAD for Mac cannot import STEP or IGES files. So looks like OP needs some additional conversion software which can convert STEP or IGES to DWG (on Mac it can be Rhinoceros)