Hello @Tobi_Huber
Here’s a screen record where you can see my approach. I think it’s easier 
Video > https://www.useloom.com/share/1c1d99a45a7b4f868ec11eae4777f18e
1. Delete the first nav
2. Open the page settings and click custom code
3. In the head area add the code from bellow
<style>
.navbar-abteilung.w-nav {
position: -webkit-sticky;
position: -moz-sticky;
position: -ms-sticky;
position: -o-sticky;
position: sticky;
top: 0px;
}
</style>
The code tells the navbar to stick when the top of the viewport reaches it.
Tell me if this works.
Piter 