Another way to skin this cat. This is very similar to Henry's,
but draw out your polyline that you want as your section line,
give it a World "Line Width Scaling" with a very thin width,
then give it a 3D Thickness (or extrude).
Subtract the Polyline from the 3D object.
Explode the 3D Object "once".
You should now have two parts.
The advantage this has over the Slice tool is that you can use polylines with arc segments.
The disadvantage, the thin section that get subtracted along the path of the polyline is lost.
Designer, Deluxe, (Professional, Expert, Basic), Platinum
Windows 10 Pro (1903), 64-bit