Hi @LeoImLeo ,

Geometric-Center works only with closed polylines and splines as stated here:
https://help.autodesk.com/view/ACDMAC/2022/ENU/index.html?guid=GUID-A782462F-F85C-4496-85A5-3D9A5454...

So you cannot use Geometric-Center OSNAP directly on 3D Solid in your drawing.
You can use 3D Object Snap to snap to the center of the face - "_zcen":
https://help.autodesk.com/view/ACDMAC/2022/ENU/index.html?guid=GUID-06D81B23-B171-4F33-920B-4609E22D...

If you need use Center of Gravity as base point, then on Mac you can only get it's approximate coordinates with MASSPROP command. In AutoCAD for Windows you can use AutoLISP routine with ActiveX interface, which is not available on Mac.