This functionality highlights the contour of the object. To apply it, select the object in the VTK Viewer, right-click on it and choose in the context menu Representation -> Feature edges.

To select, which contours should be highlighted, in the Main menu choose View -> Windows -> Feature Edges

Feature edges angle - allows to define at which minimum angle between two faces a wire is considered an edge.
Show feature edges - allows to display feature edges.
Show boundary edges - allows to display boundary edges.
Show manifold edges - allows to display manifold edges.
Show non-manifold edges - allows to display non-manifold edges.