PHP MU plugin include that disables image and iframe lazy loading included in WordPress core since 5.4. There is no need to use this unless you know you need it!

disable-core-lazyloading.inc.php

<?php
/**
 * Plugin Name:     eggMUP: Disable Browser Lazyloading
 * Plugin URI:      https://gist.github.com/ianpegg/41fb0d5df8cb55f648b42e176b152012
 * Description:     Browser-based lazyloading is great, but not yet fully supported. If you are using a JS lazy loading solution, you don't need both. This must-use plugin disables browser lazy loading that was added in WP 5.4.
 * Version:         1.0.0
 * Author:          Ian Pegg
 * Author URI:      https://eggcupwebdesign.com
 * php version 7.4.15
 * 
 * @category Must_Use_Plugin
 * @package  WordPress_Plugin
 * @author   Ian Pegg <hello@eggcupweb.com>
 * @license  GNU/GPLv3 https://www.gnu.org/licenses/gpl-3.0.txt
 * @link     https://eggcupwebdesign.com
 */

namespace EggCup\MUP\DisableCoreLazyLoading;

if (!defined('ABSPATH')) {
    exit;
}


/**
 * Register the following functions with WP action hooks/filters:
 */
add_filter(
    'wp_lazy_loading_enabled',
    __NAMESPACE__ . '\\Disable_Core_Lazy_loading',
    10,
    3
);


/**
 * Disables WP core lazy loading of iframes and images as
 * LiteSpeed's implementation is more effective - for now...
 *
 * @param Bool   $Bool_default Whether lazy loading is enabled by default
 * @param String $Str_tag_name Current HTML tag: img or iframe
 * @param String $Str_context  Current context, e.g. body content, widget
 *
 * @return void
 */
function Disable_Core_Lazy_loading($Bool_default, $Str_tag_name, $Str_context)
{
    return false;
}