Ok, so i would appraoch it like so, but it will probably require some CSS:
1. remove the header elements
2. use a Hook Element to add your element to the generate_after_primary_menu hook.
3. Set the Customizer > Layout > Primary Navigation width and inner width to Full width.
This will add the element inside the nav, so when it gets cloned for the sticky nav, then you should keep it.
I can assist with the CSS if i can see it ?
Element will now be sticky in Desktop 🙂
Content won’t be shown but that’s another question I guess.
Mobile view will not be full width so I guess I some CSS.