When you click on a link and it says "404 page not found". It means it is a broken link page.
There is no such page available any more. That particular page has been removed or the URL has been changed. It short, it is a dead end page.
Broken links are bad for search engines and also for your readers.
These 404 error pages found links can be easily detected by broken link checker software.
For those using WordPress, you can use broken link checker plugins.
As for those using Blogspot, you do not have the advantage of using plugins.
But there are free tools to check for broken links for your Blogspot blogs.
Some of them you need to download them into your PC and there are other software which you do not have to download.
You just go the site and type in your blog URL.
Free broken link checking tools no downloading required
Here are three free broken link checker tool which you do not have to download to use them.
HTML Link Checker
https://www.brokenlinkcheck.com/link-checker.php
W3C Link Checker
https://validator.w3.org/checklink
Dead Link Checker
https://theworkingwebmaster.com/tools/dead_link_checker/dead_link_checker.php