Can't resize detail view

According to tutorial, detail in layout can be resized by grabbing one of the handles in the box around the detail. But this does not work! Moving a handle crops the detail instead.
I have to change the scale of the detail to resize it - works, but very clumsy!

Sorry, it sounds like you are conflating to different things.
The Detail is a rectangle within the Layout that is a “window” into your model.
One of the Detail’s properties is the Zoom scale that displays within it.

Have a look at these tutorials to learn about it:
https://www.rhino3d.com/tutorials#drafting