In Object Manager, additionally to the drag and drop, it is now possible to assign selected objects to an existing Part/Molecule from a current selection through a contextual menu for easier Surface management.
After selecting objects in the Object Manager table or in the 3D, use the RMB contextual menu and choose New Part from selection to proceed.
NB
a volatile window will open to select the targetted Part/Molecule.
Filter searches in parts and molecules (looks only for molecules)