This WordPress mu-plugin disables php deprecated messages and warnings,

Disable-PHP-Warnings.php

<?php
/*
  Plugin Name: Disable PHP warnings
  Description: This plugin disables php deprecated messages and warnings, 
  Version: 0.1
  Author: mohsinrasool
  Author URI: https://mohsinrasool.pk


*/

// ini_set('display_errors', 'Off');
// ini_set('display_startup_errors', 0);

// ini_set('error_reporting', 0);
// error_reporting(0);
// define('WP_DEBUG', false);
// define('WP_DEBUG_DISPLAY', false);



function meti_disable_php_warnings() {
  
  ini_set('display_errors', 'Off');
  ini_set('display_startup_errors', 0);

  ini_set('error_reporting', E_ALL & ~E_DEPRECATED & ~E_NOTICE & ~E_USER_DEPRECATED & ~E_WARNING & ~E_STRICT);
  // error_reporting(E_ALL & ~E_DEPRECATED & ~E_NOTICE & ~E_USER_DEPRECATED & ~E_WARNING);
}
// add_action( 'init', 'meti_disable_php_warnings' );
add_action( 'plugins_loaded', 'meti_disable_php_warnings' );
// add_action( 'setup_theme', 'meti_disable_php_warnings' );
// add_action( 'muplugins_loaded', 'meti_disable_php_warnings' );
// add_action( 'wp_loaded', 'meti_disable_php_warnings' );
// add_action( 'wp_head', 'meti_disable_php_warnings' );
// add_action( 'wp', 'meti_disable_php_warnings' );
// add_action( 'wp_loaded', 'meti_disable_php_warnings' );