Show Site ID next to Site Title in WP Toolbar for Super Admins

site-id-wp-toolbar.php

<?php
/**
 * Display Site ID next to site name
 */
add_action( 'admin_bar_menu', function( $wp_admin_bar ) {
	// Check to make sure user is super admin
	if ( is_super_admin() ) {
		// Get site name node and Blog ID
		$site_name_node = $wp_admin_bar->get_node( 'site-name' );
		$blog_id = get_current_blog_id();

		// Don't show for network admin
		if ( ! is_network_admin() && $site_name_node && $blog_id ) {
			// Remove the default node
			$wp_admin_bar->remove_node( 'site-name' );

			// Add the new node, with values from default except for the title
			$wp_admin_bar->add_node([
				'parent' => $site_name_node->parent,
				'id'     => $site_name_node->id,
				'title'  => $site_name_node->title . ' (#' . $blog_id . ')',
				'href'   => $site_name_node->href,
				'group'  => $site_name_node->group,
				'meta'   => $site_name_node->meta,
			]);
		}
	}

	return;
}, 31 );