If a navigation menu cannot be found, the menu name is still output, orphaned in the template part details panel: <img width="919" alt="Screenshot 2023-09-26 at 11 48 22" src="https://github.com/WordPress/gutenberg/assets/846565/90694694-d05a-4429-93ff-bfe7f61b5b3c"> This looks a bit strange and should probably just be hidden.