The 404 page in your eyes may not return a 404 status code

During website diagnosis, many webmasters often check whether the website has 404 pages. Generally, the method is very simple, that is, to enter an error link for this domain name in the address bar of the search engine, check whether there is a 404 page. Is that true? 404 indicates that the page requested by the browser and the search engine does not exist or the link is incorrect. This check only shows that the user sees the 404 page, but what about the search engine? Will 404 status code be returned for this page?

First, let's take a look at the two pictures below. The 404 page in your eyes may not return a 404 status code.