Get mesh intersection points with arbitrary plane/disc

I want to be able to draw a disc around the centre of an arbitrary mesh and get the resulting 2D cross section, without using a collider for the disc/plane which forms the intersection.

As an example, here’s a disc of radius 1 around the centre of an octahedron. The cross section of both shapes is a square. What would be the simplest way to detect the points of intersection?


This sounds similar to this question. Maybe have a look at the gif i’ve linked at the end of my answer to see if that’s what you’re after.