Page template including header section

See here:

https://www.screencast.com/t/mjKVrlld3N

Ah, do I need Gutenberg to be active? I don't use this crappy editor. I hate this thing.

For Blocks yes.
If you want to use HTML then use a Hook Element - aside of the Element Type it will display the Hook and Priority options.

Ok, then I would have to write a shortcode that fetches the featured image. Tested and works. Great! Thank you very much!

Glad to hear that!