Mean crease is not am ‘operator’, but the result of a calculation (the average of all creases of the selected edges).
Search for crease will yield a result. You can also find it in the Edge menu (or with shortcut CTRL+E). Or in the context menu in Edge Select Mode (‘W’ if using Right Click Select, or right clicking in empty space when using Left Click Select).
If you have no edges selected you will not see this ‘Crease’ in Edge Data in the N-panel.
If you select more than one edge you will see your beloved ‘Mean Crease’:
