I can't get the top of the "M" to extend. I don't understand the pit about selecting the nodes at the top of the "M". When I try to drag the top of the "M" up, I am dragging a bezier curve not a straight line as shown in the tutorial illustration. Using Mac OS X Big Sur

You need to grab one of the selected nodes to move all of the selected at once. Have a look here:

Thanks Polygon. That worked.