WordPress at a glance
function is not described

get_theme_updates() WP 1.0

No Hooks.

Return

Array.

Usage

get_theme_updates();

Code of get theme updates: wp-admin/includes/update.php WP 5.2.2

<?php
function get_theme_updates() {
	$current = get_site_transient( 'update_themes' );

	if ( ! isset( $current->response ) ) {
		return array();
	}

	$update_themes = array();
	foreach ( $current->response as $stylesheet => $data ) {
		$update_themes[ $stylesheet ]         = wp_get_theme( $stylesheet );
		$update_themes[ $stylesheet ]->update = $data;
	}

	return $update_themes;
}