WordPress at a glance
function is not described

wp_admin_bar_updates_menu() WP 3.1.0

Provide an update link if theme/plugin/core updates are available.

No Hooks.

Return

Nothing (null).

Usage

wp_admin_bar_updates_menu( $wp_admin_bar );
$wp_admin_bar(WP_Admin_Bar) (required)

Code of wp admin bar updates menu: wp-includes/admin-bar.php WP 5.2.2

<?php
function wp_admin_bar_updates_menu( $wp_admin_bar ) {

	$update_data = wp_get_update_data();

	if ( ! $update_data['counts']['total'] ) {
		return;
	}

	$title  = '<span class="ab-icon"></span><span class="ab-label">' . number_format_i18n( $update_data['counts']['total'] ) . '</span>';
	$title .= '<span class="screen-reader-text">' . $update_data['title'] . '</span>';

	$wp_admin_bar->add_menu(
		array(
			'id'    => 'updates',
			'title' => $title,
			'href'  => network_admin_url( 'update-core.php' ),
			'meta'  => array(
				'title' => $update_data['title'],
			),
		)
	);
}