I'm trying to project the outline of an object onto a 2D plane

[RSEhlers]

Here are a few ways via procedural transparency, camera clipping and Booleans…

How to Do Cross Sections in Blender - Tutorial 2023

There is another tutorial on cross-sections.

Learn How to Create an Architectural Axonometric Section with Blender In Easy steps!

and an add-on…

Section Box - Cross Sections, Elevations, And Visualization

or…

section plane

Here’s a quick way for slicing in EEVEE: [slice] The slice plane can be turned off for rendering, or you set its material to Transparent and not cast shadows. Either way, I don’t see a way to cap the slice (since the AO node isn’t doing much good working only in screenspace AND forcing the same settings as the AO used in the actual rendering). Also the inside of the sliced geometry is still receiving shadows, as if the geometry isn’t cut open, so the only thing to do is tint and/or light up t…