https://apoorv.blog/breadcrumb-json-ld-hugo/

breadcrumb-links.html

{{ $pScratch := .Scratch }}
{{ range .Params.categories }}
    <p><a href="/">Home</a> > <a href="/categories/">Categories</a> > <a href="/categories/{{.}}">{{ humanize . }}</a> > {{ $pScratch.Get "title" }} </p>
{{ end }}
<p>
    {{ range $index, $breadcrumb := ($pScratch.Get "breadcrumb") }}
        {{ if ne $index 0 }}
            >
        {{ end }}
        {{ if eq $breadcrumb.url ($pScratch.Get "permalink") }}
            {{ $breadcrumb.name }}
        {{ else if eq $breadcrumb.url $.Site.BaseURL }}
            <a href="/">{{ $breadcrumb.name }}</a>
        {{ else }}
            <a href="{{ $breadcrumb.url }}">{{ $breadcrumb.name }}</a>
        {{ end }}
    {{ end }}
</p>

breadcrumbs.html

{{ $url := replace .Permalink (printf "%s" .Site.BaseURL) ""}}
{{ .Scratch.Add "path" .Site.BaseURL }}
{{ .Scratch.Add "breadcrumb" (slice (dict "url" .Site.BaseURL "name" "Home"))}}
{{ .Scratch.Add "permalink" .Permalink }}
{{ .Scratch.Add "title" .Title }}
{{ $pScratch := .Scratch }}

{{ range $index, $element := split $url "/" }}
  {{ $pScratch.Add "path" $element }}
  {{ $pScratch.Add "path" "/" }}
  {{ if ne $element "" }}
    {{ if eq ($pScratch.Get "path") ($pScratch.Get "permalink") }}
        {{ $pScratch.Add "breadcrumb" (slice (dict "url" ($pScratch.Get "path") "name" ($pScratch.Get "title")))}}
    {{ else }}
        {{ $pScratch.Add "breadcrumb" (slice (dict "url" ($pScratch.Get "path") "name" (humanize .)))}}
    {{ end }}
  {{ end }}
{{ end }}

<script type="application/ld+json">
  [{
    "@context": "https://schema.org",
    "@type": "BreadcrumbList",
    "itemListElement": [
      {{ range $index, $breadcrumb := .Scratch.Get "breadcrumb" }}
        {{ if ne $index 0 }},{{ end }}
          {
            "@type": "ListItem",
            "position": {{ add $index 1 }},
            "name": "{{ $breadcrumb.name }}",
            {{ if ne $breadcrumb.url ($pScratch.Get "permalink") }}
              "item": {{ printf "%s" $breadcrumb.url }},
            {{ end }}
          }
      {{ end }}
      ]
    }
    {{ range $index, $category :=  .Params.categories }}
      ,
      {
        "@context": "https://schema.org",
        "@type": "BreadcrumbList",
        "itemListElement": [
          {
            "@type": "ListItem",
            "position": 1,
            "name": "Home",
            "item": "{{$.Site.BaseURL}}",
          },
          {
            "@type": "ListItem",
            "position": 2,
            "name": "Categories",
            "item": "{{$.Site.BaseURL}}categories/",
          },
          {
            "@type": "ListItem",
            "position": 3,
            "name": "{{ humanize . }}",
            "item": "{{$.Site.BaseURL}}categories/{{.}}",
          },
          {
            "@type": "ListItem",
            "position": 4,
            "name": "{{ $pScratch.Get "title" }}",
          },
        ]
      }
    {{ end }}
    ]
</script>