Spiritually, being dead is a relational concept. We are not friends/family but enemies. We are not connected to or in concert with the things of God or his goodness. Sin separates us from God.
Our spiritual nature is broken, not unfunctional. It does not function as it should, and thus cannot be what it was created to do.
In my opinion, it shows that its functionality seeks other things instead of God. It’s not operating properly when propelled by the sinful nature, but it is not non-existent/dead/ non functional per se!
Doug