Export WordPress XML content acessing this file. It supports the exports of more posts than it's supported trough the panel with the same server resources.

export.php

<?php

include 'wp-config.php';
include 'wp-admin/includes/export.php';
 
ob_start();
export_wp();
$file = ob_get_contents();
ob_end_clean();
 
$fh = fopen("wordpress-" . date('Y-m-d') . ".xml", 'w');
fwrite($fh, $file);
fclose($fh);