Do you have hosting control panel with options to choose PHP version? If so, you could try to change from PHP 8 to PHP 7.4 for example. X3 works with PHP 8, but sometimes your hosting will provide different environments for different PHP versions. Since this started failing at some point without reason, the only likely change made on your server is automatically updating the PHP version.
Optionally, you can send login to details to me by private message. Click my profile. I would have preferred to avoid this, because I can't see errors from here, and would need to start diagnosing by eliminating code piece by piece. I would have emailed your hosting about this also, as they have access to error logs, and know what must have happened on your server since it was last working (php upgrades etc).