Support

That's a bug in the code of the site. It has nothing to do with the restoration.

In fact, the bug is the lowercase "h" in \helper\. This MUST be an uppercase H.

Your site worked for you before because it was hosted on a case-insensitive filesystem, most likely NTFS on Windows or APFS on macOS. When Joomla's PSR-4 autoloader was looking for the Joomla\Module\Login\Administrator\helper\LoginHelper class in the file administrator/modules/mod_login/src/helper/LoginHelper.php the Operating System's case-insensitive filesystem was able to load it from administrator/modules/mod_login/src/Helper/LoginHelper.php since case-insensitivity means that helper and Helper are the same thing.

You restored, however, to a Linux server. Linux uses predominantly case-sensitive filesystems such as Ext4. With a case sensitive filesystem helper and Helper are two different things. Therefore, when Joomla's PSR-4 autoloader was looking for the Joomla\Module\Login\Administrator\helper\LoginHelper class in the file administrator/modules/mod_login/src/helper/LoginHelper.php the Operating System's case-sensitive filesystem was NOT able to find that file since the lowercase helper directory does not, in fact, exist.

All Global Configuration settings are saved into the configuration.php file. To turn on the debug mode and error reporting when you don't have access to the site you need to edit the configuration.php file and change the $debug and $error_reporting lines to read:

public $debug = true;
public $error_reporting = 'maximum';

This will give you the full error backtrace using Symphony's error report page which is integrated into Joomla. This tells you what happened, the file and line, and even show you the lines around the error (with line numbers!) to help you understand the problem before you even edit the problem file.