Create dynamic favicon with Meta Box Plugin

single-product.php

<?php
/**
 * The template for displaying all single posts
 *
 * @link https://developer.wordpress.org/themes/basics/template-hierarchy/#single-post
 *
 * @package Justread
 */

get_header(); ?>

	<div id="primary" class="content-area">
		<main id="main" class="site-main">

		<?php
		while ( have_posts() ) : the_post();

			get_template_part( 'template-parts/content', 'single' );

			$favicon_site = get_site_icon_url();

			$favicon = rwmb_get_value('favicon', array( 'size' => 'thumbnail' ));

			if (isset($favicon) && $favicon !== null) {

				$favicon_url = $favicon['url'];

			} else {

				$favicon_url = $favicon_site;

			}

			the_post_navigation();

			// If comments are open or we have at least one comment, load up the comment template.
			if ( comments_open() || get_comments_number() ) :

				comments_template();
			
			endif;

		endwhile; // End of the loop.
		?>

		</main><!-- #main -->
	</div><!-- #primary -->
	<script>
		(function() {
			var favicon = '<?php echo $favicon_url; ?>';
		    var link = document.querySelector("link[rel*='icon']") || document.createElement('link');
		    link.type = 'image/x-icon';
		    link.rel = 'shortcut icon';
		    link.href = favicon;
		    document.getElementsByTagName('head')[0].appendChild(link);
		})();
	</script>
<?php
get_footer();