Hi there!
Sorry for the inconvenience.
Have you updated your system plugin of Helix3 recently? If yes, is it possible for you to revert back to your last working backed up version?
The Shopin template doesn't get the latest version of helix3 and Joomla 4 compatibility update because of the dependency on the third party shop management extension J2store. Once the template gets an update you can perform the update operation, until then kindly do not update the system plugin of your framework.
Best Regards