Once the user accesses an invalid URL, WordPress will look for a valid 404 template. The 404 template is generated by the 404.php file of the theme, so it will be a theme-specific page.

If a valid 404.php file is not available in the theme, WordPress will load the default 404 content within the core with a basic message and search form.

In this scenario, we have created a 404.php file in the child theme using the 404.php file of the parent theme. Now, WordPress will look for the 404.php file within the child theme, instead of the parent theme. In the custom 404 template, we removed the original header of the Twenty Twenty template and changed the message to the following:

<?php _e( 'The page you were looking for could not be found. It might have been removed, renamed, or did not exist in the first place.Maybe try a search or view our posts?', 'twentytwenty' ); ?>

Then, we used the code from the previous recipe to display the post list on a 404 page. However, the following code only limits the post list to three entries as this is a 404 page and too much information can discourage the user to browse the site:

<?php $post_list = new WP_Query(array('post_type'=>'post', 'post_status'=>'publish', 'posts_per_page'=> 3 )); ?>

The other parts of the code are exactly same as they are for the post-grid.php file.