The content isn’t served by Netlify. This certificate, as with the Let’s Encrypt free certificate, only covers content served by Netlify.
The Revue documentation uses Cloudflare because the content is proxied through Cloudflare.
You may need to look at using Cloudflare for DNS in order to achieve what you want. Do note that if you choose this route, you will need to ensure the domain(s) on Netlify are not proxied as outlined in this support guide