Google’s John Mueller answered a question on Reddit about what to do about the thousands of 404 errors reported in Google Search Console.
John’s answer clarified how to approach the Search Console Page Indexing report with regard to the 404 errors listed there.
404 Error Response
The 404 error response is a message from a server to the crawler (or a browser) telling the the crawler that the server encountered an error in fetching the requested webpage because it does not exist.