If you use draw.io in Confluence and Jira Cloud, you only need to license it in Confluence Cloud for it to work in both.
Follow this process detailed in our documentation exactly to install draw.io in both instances. The app will then work in both your Jira Cloud and Confluence Cloud instances, but you will only be billed for the Confluence Cloud version.
Fore more general info on draw.io for Confluence or Jira, please refer to our draw.io webpage.
And some great blogposts! Blog - draw.io