Hi Oliver. 
Instead of having the same header image for all blog posts, I wanted the featured image to appear in the header. So I decided to create a new post template with your template builder. Unfortunately, the featured image doesn't show up, it's a blank space instead (screenshot). Thinking it was an Elementor issue, I contacted their tech support. I followed their troubleshooting steps without being able to solve the problem. I then got the idea to use their theme builder to create a blog post template and to my surprise, the featured image was displayed (screenshot). While I chose to use this template as a base for blog posts, the hero section appears framed instead of full width (screenshot).

It would be great if you could resolve this issue about the featured image not appearing using your template builder.

Thanks Oliver.