Error in CRM_Contact_Form_Relationship->setEmploymentRelationship() when saving an edited relationship
The error claims that civi is not able to find the isCurrentEmployerNeedingToBeCleared() function in CRM/Contact/BAO/Relationship.php file.

It is not possible as this change was merged recently with the function being declared and used in the same PR https://github.com/civicrm/civicrm-core/pull/12032.

Quite possible that one of your custom extension OR custom php directory might be overriding CRM/Contact/BAO/Relationship.php file and is not updated to the latest 5.x version.

If you can check and update that file or simply disable the extension that overrides the file - the error should be fixed.