Hi Tanguy, there is not a display mode in MoI for showing undercuts but there is a Silhouette command that can generate curves at places where there are undercuts.

So for example with an object that has undercuts like this:



You can select it and run Construct > Curve > Silhou :



Set the option for View : Top and it will generate silhouette curves in the z axis direction which will be parting lines and also be present at undercut areas:



- Michael