Triangles are certainly a good example.

For example, the boom of a crane is welded into a triangle with iron bars.

Or the details of the tower are triangular.

The quadrilateral is unstable.

Such examples are rare.

One that comes to mind is the vendor's push-pull folding door.

Quadrilateral with welding

Pushing away is a long diamond.

Put it up, it is a short diamond.

This makes use of the unstable and changeable characteristics of quadrilateral.