Get the list of plugin update URLs on a WordPress site

wp-plugin-update-urls.php

<?php
/**
 * Get the list of plugin update URLs for a site, so they can be downloaded and tested locally/on staging before installing on production.
 *
 * Often plugins' licence keys can only be installed on one site, production is obviously chosen, then the plugin update
 * can only be downloaded on production.
 */

/** @var array<string, string> $plugin_update_urls The plugin update download links keyed by plugin basename. */
$plugin_update_urls = array();

/**
 * The plugin update data (which drives the yellow boxes on plugins.php).
 *
 * @see wp_update_plugins()
 * @see wp-includes/update.php
 *
 * @var stdClass{last_checked:string,response:array,translations:array,no_update:array,checked:array<string,string>} $plugin_updates
 */
$plugin_updates = get_site_transient('update_plugins');

/**
 * Get all valid plugin update URLs.
 *
 * @var string  $plugin_basename
 * @var stdClass{new_version:string, stable_version:string,name:string,slug:string,url:string,last_updated:string,homepage:string,package:string,download_link?:string,sections:stdClass{description:string,changelog?:string},banners:stdClass{high:string,low:string},icons:string} $values
 */
foreach ($plugin_updates->response as $plugin_basename => $values) {
    if ( filter_var($values->package, FILTER_VALIDATE_URL) ) {
        $plugin_update_urls[$plugin_basename] = $values->package;
    }
}

// Filter out plugins on the .org repo.
array_filter( $plugin_update_urls, function( string $url ): bool {
    return 0 !== strpos($url,'https://downloads.wordpress.org');
} );