tableofcontents maxdepth directive not applied

[ZviBaratz]

Describe the problem

The table of contents rendered by the tableofcontents directive shows only one level, even when the maxdepth parameter in the book's _toc.yml is set to some higher number.

Link to your repository or website

https://zvibaratz.github.io/phd/content.html

Steps to reproduce

1. Create a book with some "deep" headers and a _toc.yml such as:

   format: jb-book
   root: front
   chapters:
   - file: abstract
   - file: content
   options:
   numbered: true
   maxdepth: 4
   sections:
   - file: lists
   - file: chapters/introduction
   ...

The version of Python you're using

3.9.9

Your operating system

Linux (Kubuntu)

Versions of your packages

Jupyter Book      : 0.12.1
External ToC      : 0.2.3
MyST-Parser       : 0.15.2
MyST-NB           : 0.13.1
Sphinx Book Theme : 0.1.7
Jupyter-Cache     : 0.4.3
NbClient          : 0.5.9

Additional context

The issue is opened following the discussion in executablebooks/meta#592.

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[ZviBaratz]

This is resolved with titlesonly set to false.