Unfortunately, Joplin does not allow us to view a list of all notes from the root notebook or even from a notebook that has nested notebooks. We need to go to the very end notepad to see the notes that belong to it.
Maybe there is some kind of plugin for displaying. Please share the information.
The notebook: search filter includes notes in nested notebooks. Use it with the search bar, Goto Anything (Ctrl+P), and/or plugins.
For example: install the Note Overview plugin on desktop. Then, add the below to a new note, replacing name with the desired notebook name:
<!-- note-overview-plugin
search: notebook:"name"
fields: title
listview:
text: "{{title}}"
-->
Generate the list with Tools > Update note overview. It can be viewed on desktop or mobile. The desktop plugin can also generate and update the list at regular intervals.
If you need more customization, visit the above link.
If your desktop menu bar is hidden, press Alt to show it temporarily, or Ctrl+Shift+M to toggle it. Otherwise, I wouldn't know why you don't see that option without more info.
However, with the plugin's 5 minute default update interval, it should have generated your list by now.