The Copy as 3MF is not enabled even after selecting the structure in my ChemDraw 21.x

ChemDraw Prime, as well as ChemDraw Professional, does not have these features [3MF (Ball and Stick) and 3MF (Stick)]

For these features, you need a ChemOffice + Cloud license.

Once you activate the product using ChemOffice + Cloud activation code the 3MF functions are enabled.