Fix url when wp-content and mu-plugins are added as symlink.

fix-symlink-url.php

<?php
/**
 * Fix url when wp-content and mu-plugins are added as symlink.
 */
add_filter( 'plugins_url', function ( $url ) {
	// Replace wp-content absolute path.
	if ( defined( 'WP_CONTENT_DIR' ) && is_link( WP_CONTENT_DIR ) ) {
		$mu_content_dir_path = dirname( __DIR__ );
		$url                 = str_replace( 'plugins' . $mu_content_dir_path, '', $url );
	}
	// Replace vip-mu-plugins's absolute path.
	if ( defined( 'WP_CONTENT_DIR' ) && is_link( WP_CONTENT_DIR . '/mu-plugins' ) ) {
		$mu_plugin_path = realpath( WP_CONTENT_DIR . '/mu-plugins' );
		$url            = str_replace( 'plugins' . $mu_plugin_path, 'mu-plugins', $url );
	}

	return $url;
}, 1 );