Are Collapsible horizontal navigation bars ever used?

There is an ask to have a collapsible horizontal navigation bar. This would be below the main horizontal navigation. This is not standard imo. And poor user experience because it is so uncommon. The reasoning is to allow more page real-estate. This would mean that the page content ( breadcrumb, title etc ) would shift or jump up everytime the horizontal navigation header is collapsed/exanded.

Are there any examples you have seen? And is there any write ups on why this is poor ux?

Thanks!