Mermaid doesn't work

[nicfab]

Hi!
Starting from the file single.html, which is under themes/PaperMod/layouts/_default, I edited it adding the following Mermaid code

{{ if .Page.Store.Get "hasMermaid" }}
  <script src="https://cdn.jsdelivr.net/npm/mermaid/dist/mermaid.min.js"></script>
  <script>
    mermaid.initialize({ startOnLoad: true });
  </script>
{{ end }}

I retrieved that code from the Hugo website, here https://gohugo.io/content-management/diagrams/#mermaid-diagrams
I put the modified file single.html in /layouts/_default/, leaving the original single.html under themes/PaperMod/layouts/_default.

Now the files single.hml under /layouts/_default/ has the following lines:

{{- define "main" }}

<article class="post-single">
  <header class="post-header">
    {{ partial "breadcrumbs.html" . }}
    <h1 class="post-title">
      {{ .Title }}
      {{- if .Draft }}<sup><span class="entry-isdraft">&nbsp;&nbsp;[draft]</span></sup>{{- end }}
    </h1>
    {{- if .Description }}
    <div class="post-description">
      {{ .Description }}
    </div>
    {{- end }}
    {{- if not (.Param "hideMeta") }}
    <div class="post-meta">
      {{- partial "post_meta.html" . -}}
      {{- partial "translation_list.html" . -}}
      {{- partial "edit_post.html" . -}}
      {{- partial "post_canonical.html" . -}}
    </div>
    {{- end }}
  </header>
  {{- $isHidden := .Params.cover.hidden | default .Site.Params.cover.hiddenInSingle | default .Site.Params.cover.hidden }}
  {{- partial "cover.html" (dict "cxt" . "IsHome" false "isHidden" $isHidden) }}
  {{- if (.Param "ShowToc") }}
  {{- partial "toc.html" . }}
  {{- end }}

  {{- if .Content }}
  <div class="post-content">
    {{- if not (.Param "disableAnchoredHeadings") }}
    {{- partial "anchored_headings.html" .Content -}}
    {{- else }}{{ .Content }}{{ end }}
  </div>
  {{ if .Page.Store.Get "hasMermaid" }}
  <script src="https://cdn.jsdelivr.net/npm/mermaid/dist/mermaid.min.js"></script>
  <script>
    mermaid.initialize({ startOnLoad: true });
  </script>
  {{ end }}
  {{- end }}
  
  <footer class="post-footer">
    {{- if .Params.tags }}
    <ul class="post-tags">
      {{- range ($.GetTerms "tags") }}
      <li><a href="{{ .Permalink }}">{{ .LinkTitle }}</a></li>
      {{- end }}
    </ul>
    {{- end }}
    {{- if (.Param "ShowPostNavLinks") }}
    {{- partial "post_nav_links.html" . }}
    {{- end }}
    {{- if (and .Site.Params.ShowShareButtons (ne .Params.disableShare true)) }}
    {{- partial "share_icons.html" . -}}
    {{- end }}
  </footer>

  {{- if (.Param "comments") }}
  {{- partial "comments.html" . }}
  {{- end }}
</article>

{{- end }}{{/* end main */}}

Unfortunately, Mermaid doesn't work.
Where was I wrong?