Force no-cookie domain for Youtube embeds

who-youtube-embed-nocookie.php

<?php
/*
Plugin Name: Force no-cookie domain for Youtube embeds.
Plugin URI: https://whodunit.fr
Description: Forces no-cookie domain on every Youtube embed.
Author: Whodunit
Version: 1.0
Author URI: https://whodunit.fr
*/

/**
 * Filters embed URLs to force replace domain with no-cookie.
 * 
 * @param string|false $cache The cached HTML result, stored in post meta.
 */
function who_force_youtube_nocookie_domain( $cache ) {
	// Use youtube-nocookie.com for YouTube embeds.
	if ( str_contains( $cache, 'https://www.youtube.com/embed' ) ) {
		$from  = 'src="https://www.youtube.com/embed/';
		$to    = 'src="https://www.youtube-nocookie.com/embed/';
		$cache = str_replace( $from, $to, $cache );
	}
	return $cache;
}
add_filter( 'embed_oembed_html', 'who_force_youtube_nocookie_domain' );