Ok, we now have the contour that we still need to smooth out. However, so that we can check the deviation from the original line at any time, we must safe the starting line.
It's very simple:
select the desired line
“duplicate" in the "Edit" menu
chose "Fill and Stroke" in the right-hand window
select "Stroke Paint" in the tab bar below
Select HSL
select an eye-catching color for "H"
set a medium value for "S" and "L"
set a high value for "A"
finally, set "lower to bottom" in the "Object" menu
This gives you an eye-catching line in the background. So you can always see every change clearly. And because it is in the background, it is not so easy for you to select it.