A simple WordPress plugin that shows the last modified date of a post. Visit https://www.davidangulo.xyz/ for more information.

column.php

<?php
/*
Plugin Name: Custom Column Plugin Example
Plugin URI: https://www.davidangulo.xyz/portfolio/
Description: Add a custom column on WordPress posts.
Version: 1.0.0
Author: David Angulo
Author URI: https://www.davidangulo.xyz/
License: GPL2
*/

add_filter("manage_posts_columns","column_head");
function column_head($columns) {
	$columns["custom_column"] = "Last Modified Date";
	return $columns;
}

add_action("manage_posts_custom_column","column_content",10,2);
function column_content($column_name,$post_ID) {
	if ($column_name == "custom_column") {
		echo "Last Modified<br><abbr title=".get_the_modified_time("Y/m/d").get_the_modified_time("h:i:s a").">".get_the_modified_time("Y/m/d")."</abbr>";
	}
}

//Visit the tutorial for more information
//https://www.davidangulo.xyz/website-development/how-to-add-custom-column-in-wordpress-post/