Hello Friends,

     How to fix massive 404 pages?

Fair use a redirect code and send those 404 pages toward main page.

The best way to handle 404s is to eliminate the problem that is causing them on your website in the first place.

Organic search results are listings on search engine results pages that appear because of their relevance to the search terms, as opposed to their being advertisements. In contrast, non-organic search results may include pay per click advertising.

best to convert that pages to 410 status code so that google will delete automatically once its get 410.

Retry the web page by pressing F5, clicking/tapping the refresh/reload button, or trying the URL from the address bar again. ...
Check for errors in the URL. ...
Move up one directory level at a time in the URL until you find something. ...
Search for the page from a popular search engine.