I think Matt Cooper takes a too narrow definition of “metabolism” as a rather dull process of material exchange that occurs within a cell. From my reading, as a non-specialist, Marx was using the term in a broader sense as the material and ultimately purposeless means by which complex order emerges from disordered matter.

This guide is designed to help understand the central ideas in Kohei Saito, Karl Marx’s Ecosocialism: Capital, Nature, and the Unfinished Critique of Political Economy. New York: Monthly Review, (2017)