Right, no marquee other than floor plan and 3D, and you cannot move the cutaway lines.
An alternative that might work for you, if your computer is decent, is to create a slab that is big and thick enough to cover the area that you want to show, and do a solid element 'intersection' operation, and then move the slab up as needed to show other cuts.
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB