In my following YouTube video, David Poulton commented that the Stroke1:Center is not available in the context menu, most likely it's due to clicking the wrong place.
If you right click the stroke, you will not see the Stroke1:Center in the menu.
When you right click the center point control
You should see a new item "Stroke1: Center" appears at the bottom of the context menu:
Alternatively, you can also go to the inspector, in the Modifiers tab, right click the Center parameter and choose "Modify With", "Tracker Position"
Hope this clears the confusion, thanks for reading!
Essential Video Editing