Sitemap URL has no internal links
What this means
The URL is submitted in the sitemap but nothing on the site links to it. Orphan pages are discoverable only via the sitemap, receive no internal link equity, and read to Google as low-priority — a sitemap entry is a hint, not a substitute for navigation.
How to fix it
Link the page from a relevant hub, category or navigation surface. If the page is not worth linking to, remove it from the sitemap.
Fix effort
This check needs review: the change can be drafted for you, but a person has to approve the wording or choose the target before it ships.
Authoritative source
https://developers.google.com/search/docs/crawling-indexing/links-crawlable
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