If I create a Nintex workflow and have it start automatically when an item is added, then whenever I create a Document Set, or add a file to it, the workflow runs. I can run the workflow just on a Document Set manually. How can I configure the workflow so that it automatically starts only when a Document Set is added to the Library?
So you could look at starting the workflow conditionally based on Content Type, I'm fairly sure you can do this, but I haven't got on-prem available to me to confirm. Otherwise, using a site reusable workflow will allow you to target a specific content type for the workflow to start on.