Google is open about the fact that it doesn’t index all the pages it can find. Using the Google Search Console, you can see the pages on your website that are not indexed.
Google Search Console also provides you with useful information about the specific issue that prevented a page from being indexed.
These issues include server errors, 404s, and hints that the page may have thin or duplicate content.
But we never get to see any data showing which problems are the most common across the whole web.
