What are software 404 and 404 errors and what are the differences between them_HTML/Xhtml_Webpage Production

First of all, what is 404 and soft 404
404: Simply put, when the user enters a link to a page that does not exist, the returned page will be represented by a 404 code.
Soft 404: Soft 404 means that when the page visited by the user does not exist, it will return not a 404 error code, but a 200 code. Guide users to continue accessing the website.
I think everyone has seen their differences:
404: Returns a 404 error page to the user, with the HTTP status code 404;
Soft 404: Returns an error prompt page to the user, with the status code 200 ;
So under what circumstances will a soft 404 appear?
Generally, we divide it into:
1: Server configuration error;
2: Website program or template error;
3: The website is caused by malicious attacks;
4: Website administrator error cause.
How to deal with soft 404, at this time we can use the robots.txt file or nofollow to prevent the crawler program from crawling the pages you do not want it to crawl. For ordinary users, soft 404 will inevitably lead to a high bounce rate of the page. In order to achieve a better user experience, we can appropriately modify the soft 404 error prompt page instead of returning to the system default page or even the homepage of the website.