@papart -- Yeah, I did not get that from your original description. Sorry.
What you're doing there in your example is a much better solution than cramming those features into the navigation stack, believe it or not. You're using the modular stacks in Foundry to create a complex layout, which is something I love!
Here's an example of this modular system -- there is a Margins stack in Foundry. This stack serves a very specific purpose -- provide responsive margins and padding that can be set at each of the three breakpoints. With this stack in Foundry it means that you can use those features with all of the other Foundry stacks. Each stack does not need to have those margins and paddings settings built-in to them. This helps to keep down bloat of the software, as well as allows you more flexibility over how your pages, and project as a whole, are designed. This modular experience is something I strive for in Foundry.
Using this modular setup you've built a more complex navigation that you can tweak for each breakpoint and then reuse throughout your project with Partials.