No way to manage menus in 6.1.1?

I’m running 6.1.1 and decided to go all in and use the Twenty Twenty-Three theme. The navigation block has me a little confused. There’s an option to use menus (presumably importing legacy menu data), but the “edit menus” option takes you to a page where… you can’t edit the menu.

What’s the relationship between the navigation block and “menus” in the sidebar? How do we go about creating or editing menus? For example, if I want to add a second level menu, how do I go about doing that using the block editor?

Thanks for any help.