Can't get rid of lastmod in sitemap (multilang site)

The problem:
I can’t remove <lastmod> from the main sitemap under the root.

My Hugo is multilang, so it wont create a typical sitemap with all the post URLs under the root, instead it will list sitemap URLs for each language. This is how it looks like:

I highlighted on yellow the part I am trying to get rid of - the <lastmod>. I managed to remove it from the sitemap for each language sitemap by exposing the sitemap template that currently sits in layouts/_default/sitemap.xml and looks like this:

{{ printf "<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\"?>" | safeHTML }}
<urlset xmlns=""
  {{ range .Data.Pages }}
    {{- if .Permalink -}}
    <loc>{{ .Permalink }}</loc>{{ with .Sitemap.ChangeFreq }}
    <changefreq>{{ . }}</changefreq>{{ end }}{{ if ge .Sitemap.Priority 0.0 }}
    <priority>{{ .Sitemap.Priority }}</priority>{{ end }}{{ if .IsTranslated }}{{ range .Translations }}
                hreflang="{{ .Language.Lang }}"
                href="{{ .Permalink }}"
                />{{ end }}
                hreflang="{{ .Language.Lang }}"
                href="{{ .Permalink }}"
                />{{ end }}
    {{- end -}}
  {{ end }}

So that’s good and I am half-way home.

Solutions I tried:
Creating additional template for sitemap with name layouts/_default/home.sitemap.xml - it did not work.

How can I remove the lastmod for the root sitemap for multilang site?

UPDATE: I think I managed to expose the main sitemap by creating additional file layouts/_default/sitemapindex.xml, however, I am having trouble populating it correctly so it can look exactly as on the screenshot above minus the line.

The embedded sitemapindex template:

Remove lines 6-8.

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