Excel must be installed on the computer which you are performing the export.
Suggest you check the system requirements for the version of QlikView in use in your environment Check the section QlikView/Microsoft Office Supported Platforms. If Office 365 is listed in this section, then it is supported. If not listed, then it is not supported.
Hope this helps
This is the response I got from Qlik
Unfortunately current QlikView is not supporting office 365 platform, the office components has to be installed locally to enable export.
However, we do have something under development at the moment which call Office 365 Connector For QlikView & Qlik Sense from QVSource connector.