Progress!
It turns out that from TextEdit a control click will offer Create Event [in Calendar.app] as the top choice. No need to use the Services Menu.
No such choice when control clicking in Safari, but you can choose New TextEdit Window Containing Selection. Then you can use the above.
I tried Is it possible to trigger a Macro in regular right-click context menu? - #5 by NaOH with no luck.
My simple macro works from the Keyboard Maestro menubar.