Hi Alicja,
You don’t need to use layout element or navigation block, just use the default navigation.
1. Go to customizer > layout > primary navigation, set navigation location
to float right
.
2. Add the button. You can use a block element:
https://docs.generatepress.com/article/block-element-overview/
https://docs.generatepress.com/article/block-element-hook/
Set entire site
as its location, set menu_bar_item
as hook name.
Once it’s done, come back to us and attach your site link, we will provide custom CSS to center the navigation.
Let me know 🙂