WordPress Initialization MU-Plugin (Must Use Plugin)

init-plugin.php

<?php
/**
 * Plugin Name: Initialization Plugin
 * Plugin URI: https://gist.github.com/idokd/224dec722a22b664c59e8d6ec221d997
 * Description: Plugin to hook and define necessary functions before other all other plugins
 * Version: 1.0.0
 * Author: Ido Kobelkowsky
 * Author URI: https://github.com/idokd
 */

$thememuplugins = get_stylesheet_directory() . '/mu-plugins.php';

if ( file_exists( $thememuplugins ) ) require_once( $thememuplugins );

This is intended to when you require to override specific functions before all other plugins, and you wish to have those functions inside your theme folder so for example

you create a PHP file: /wp-content/themes/{{your-theme}}/mu-plugins.php

and inside you can override specific functions

<?php
function overriding_some_function() {
    // your code here
}

this is when plugins use function_exists() before declaring the function, so they basically allows overriding those functions.