Hi Leonardo,
When using buttons in the header, they won’t collapse into a hamburger icon on mobile, but navigation block will.
The navigation block is a WP core block, the theme has no control over it.
However, for a simple layout like this, I don’t think you need to build a block element – site header.
You can achieve this by using the default GP header with some CSS, here’s an example on how to do that.
https://docs.generatepress.com/article/adding-buttons-navigation/