Vertical menu with full screen background image

Hi there,

tricky one without custom development.
You could use a Header Element to display the full screen container with a background image:

https://docs.generatepress.com/article/header-element-overview/

Then to add the menu, you could try this plugin:

https://en-gb.wordpress.org/plugins/widget-shortcode/

Add the shortcode it provides in the Header Element Content.
You can then add a Navigation Menu Widget to that area.

That would provide the basics.

Thank you very much David!
You have been a great help to me!

Glad to hear that!