layouts/_default/sitemap.xml

<!-- internal template -->
{{ printf "<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\"?>" | safeHTML }}
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xhtml="http://www.w3.org/1999/xhtml">
{{- range where (where .Pages ".Params.Headless" "ne" true ) "Sitemap.Disable" "ne" true -}}
{{-  if .Permalink }}
  <url>
    <loc>{{ .Permalink }}</loc>
    {{ if not .Lastmod.IsZero -}}
      {{- $ISO8601 := "2006-01-02T15:04:05-07:00" -}}
      <lastmod>
        {{- .Lastmod.Format $ISO8601 | safeHTML -}}
      </lastmod>
    {{- end }}
    {{ with .Sitemap.ChangeFreq -}}
      <changefreq>{{ . }}</changefreq>
    {{ end -}}
    {{ if ge .Sitemap.Priority 0.0 -}}
      <priority>{{ .Sitemap.Priority }}</priority>
    {{ end -}}
    {{ if .IsTranslated -}}
      {{- range .Translations -}}
        <xhtml:link rel="alternate" hreflang="{{ .Language.LanguageCode }}" href="{{ .Permalink }}" />
      {{- end }}
    <xhtml:link rel="alternate" hreflang="{{ .Language.LanguageCode }}" href="{{ .Permalink }}" />
  {{   end -}}
  </url>
{{-  end }}
{{- end }}
</urlset>