Page not found 404 is a common error when someone tries to access not existing page. Often resources being moved around the web servers and their links reaming intact pointing to the old content results in such 404 errors.
Webservers like NGINX have default “404 not found” webpages which are bland to put it mildly. They look like something from the late 90s is trying to be informative.
This can be changed for any website running wordpress on linux machines, ubuntu with lamp stack or other servers.
Very easy to use plugin for adding such functionality to a wp website is Colorlib 404 Customizer which has many templates to select from. Provides well organized options to put your personal touch to the already custom 404 not found pages.
Install it the usual way you install your wp plugins and have a look at its configuration options. That’a nice, often neglected extra of a website (custom 404 page) but it’s available so why not use it for a change.