And just to clarify a bit more - for the first case like Pilou shows above, it's more normal in MoI to draw a curve object and use Boolean Difference to cut the base solid by the curve directly rather than doing an extrusion. Booleans will automatically extrude 2D curves used as cutting objects out into extrusions that go all the way through the object so you don't need to extrude them yourself in that case.

So for example if you have a solid and a curve like this:




Run Construct > Boolean > Difference to get this result, no extrude is needed for this case of cutting all the way through an object:



- Michael