Following the documentation and taking inspiration from how it's done in the Material for MkDocs own documentation, I am trying to set up a Usage section which should point to its own index.md and have more pages below as subsections.

Here is the excerpt of my navigation settings:

nav:
  - index.md
  - Usage:
      - usage/index.md
      - usage/base64.md
  - javadoc.md
  - release-notes.md

However, the navigation is rendered as:

where the bold Usage entry isn't clickable, and there is one more redundant but clickable Usage entry.

What am I doing wrong?

Reference:

• mkdocs.yml
• usage/index.md