When a page is missing from Google, the cause is almost always one of three: Google cannot reach the page, the page carries an indexing restriction, or Google treats it as a copy of another page. Go through the points below in this order.
1. See what Search Console says
Open URL Inspection in Search Console and paste the exact address of the page. The tool tells you whether the page is in the index and, if not, why.
Make sure you are inspecting the right address. To Google, http and https, www and non-www, and addresses with and without a trailing slash are different pages.
2. Can the page be reached?
Open the page in a private browser window where you are not logged in. If you see a login page, an error or different content from what you see as an administrator, Google sees the same.
The page must return status code 200. A redirect, a 404 or a server error explains the absence.
3. Is there a block on the page?
There are two kinds of block, and they are often confused. Robots.txt stops Google fetching the page. Noindex allows fetching but forbids showing the page in search results.
In WordPress the most common cause is the setting “Discourage search engines from indexing this site”, left on after development. Also check the page-level setting in your SEO plugin.
4. Does Google treat the page as a copy?
If two pages are almost identical, Google picks one of them. Search Console shows which address Google has selected as the canonical.
If the choice is wrong, check the page’s own canonical tag and whether internal links and the sitemap point to the right address.
5. Is there enough content of its own?
Google may leave out a page that has almost nothing on it or repeats the content of other pages. If the content loads only with JavaScript, check the rendered view in URL Inspection to see that the text really appears.
6. Can Google find the page?
There must be at least one ordinary link to the page from another page, and it belongs in the XML sitemap. A page nothing links to is almost invisible to Google.
7. Fix it and request a recheck
Once you have fixed the cause, request indexing in URL Inspection. It speeds things up for a handful of pages. Indexing can still take from days to weeks.
If the page still does not appear after the fix, or the problem affects many pages, there is usually a structural fault. Finding it is technical SEO.