Can I cut a mesh?

Is there a way to cut a mesh- not dynamically, just remove parts of it to add to the graphics? Simple stuff like removing a rectangle from a wall to make way for an opening in a door. I am aware we can already cut holes in terrains.

This is broadly called CSG:

There is some support in ProBuilder for this.

It will almost always be easier to pre-author your content than to try and write code to author it on the fly.

I guess I will have to check it out, then.