Compare your sitemap URLs against an internal crawl from your Start URL. Pages in the sitemap but not discovered by internal links are flagged as potential orphans.
An orphan page is a page with zero internal links pointing to it from anywhere else on the same site. Because crawlers discover pages by following links, orphans are hard to find, crawl, and rank.
How to fix: Link orphan pages from relevant hubs, category pages, or related articles. If a page isn’t needed, consider removing it from the sitemap or redirecting it.