5 Choose any line of the object, press "#complexSection"
6 your model should be shown upper object chooser
7 mark the chooser for the cutting profile, choose in modeltree cuttingprofile sketch
8 sketch/sketch should be shown in cutting profile chooser

Making a #ComplexSection with #Freecad @FreeCAD

1 Make a Sketch with the cutting profile

2 Open #TechDraw Workbench, make a new page

3 choose object for 2D projection,

4 Result should look like this