In the manual and Help file, it says:
If you’d like to convert an existing smart group into a smart rule, ⌃-click the desired smart group, hold the ⌥ key, and choose Duplicate as smart rule.
I can’t find any “Duplicate as smart rule” selection in the context menu or its “Duplicate to” submenu. The only things that appear to change when I hold the Option key are the Open and Move to Trash selections. I’ve tried ^-clicking the smart group icon in the item list and in the sidebar. Am I not looking in the right place?