Hey Peter,

Unfortunately, featured image works only with blog posts. For static pages, you may want to add images in the content section of the page.

Adding featured image to the static page would need adding custom PHP code to the template. You can paste code from that link to the 27th line of your Child Themes’ page.php file:

https://pastebin.com/bW19c0jR

Cheers,
Piotrek