Hi Ralf,
I can see the navigation in your other pages, except the homepage.
It’s likely been disabled by a layout element or the layout metabox in the page editor.
You can check these 2 places:
1. Layout element: appearance > elements, check if there’s a layout element which includes the front page in its locations, if so, uncheck the navigation box under the disable elements tab.
2. Go to the homepage page editor, in the toolbar on the right side, and check if you chose to disable the navigation from there.
https://docs.generatepress.com/article/layout-metabox-overview/#where-is-it
Let me know π