The error you’re seeing:
Call to undefined method stdClass::get()
occurs because the code is trying to call $object->get('property') on a plain stdClass object. In PHP, stdClass objects don’t have a get() method — you can only access their properties directly using ->property.
In this case, the error comes from:
JRoot/administrator/templates/atum/html/com_templates/templates/default.php:100
You should check that line and either access the property directly, like $object->property, or wrap the object in a Joomla Registry if you need to use the get() method.
Making this change should resolve the “undefined method get()” error.
Thanks.