The Magnet tool has been disabled from 3.8.6 because this tool was merged to the Lathe tool.
This tool is similar to the Vertex Snapping tool but it works with faces in the designer object. A vertex of a face consisting of a designer object can be snapped to an another vertex to the designer object using this tool.
The Magnet tool can be combined with The lathe tool very well to position the profile cutout.