When do modernization rules decide API, rewrite, or retain?

We want a rule that says this operation becomes an API and that one stays. The rules screen has nothing to classify. Why?

Rules and routing run after operations exist. They classify how each discovered operation should move next, including API, rewrite, or retain, and they manage the gateway route lifecycle: register, approve, publish, unpublish. Apply them to operations you have saved. An empty operation list has nothing to route.