web/_includes/toc.html

{% assign enable_toc = false %}
{% if site.toc and page.toc %}
  {% if page.content contains '<h2' or page.content contains '<h3' %}
    {% assign enable_toc = true %}
  {% endif %}
{% endif %}

{% if enable_toc %}
  <section id="toc-wrapper" class="ps-0 pe-4 mb-5">
    <h2 class="panel-heading ps-3 pt-2 mb-2">{{- site.data.locales[include.lang].panel.toc -}}</h2>
    <nav id="toc"></nav>
  </section>
{% endif %}