How do I make a cube's collision work inside out

You’ve got that correct! The method from the video only adjusts face normals and does nothing to collisions. If you’d like to add, edit, or remove collisions from an object that’ll be a bit different.

If you’d like to change or override collisions on a static mesh you’ve brought in you can go over to the details tab and enable custom collision here and choose a mesh you’d prefer, or even build one with primitives.
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