This operator (Alt + D) allows users to explicitly create a linked copy of a group node (same current behaviour for the Duplicate operator). The duplicate operator (Shift + D) now takes the new User Preference duplicate data option for Node Tree into account. It is by default disabled, leading to no functional change for users. Although we could make in the future make this option "on" by default, to make it consistent with the rest of Blender we do not at the time. Differential Revision: https://developer.blender.org/D16210