hugo  --printUnusedTemplates

stdout 'Template _default/list.html is unused'

-- hugo.toml --
disableKinds = ["taxonomy", "term", "RSS", "sitemap", "robotsTXT", "404", "section", "page"]
baseURL = "https://example.org/"
-- layouts/index.html --
Home.
-- layouts/_default/list.html --
{{ errorf "unused template: %s" .Kind }}