The excel driver used by InfraMarker doesn't export the geometry. Currently, if you export a point dataset the resulting XLSX will contain the latitude and longitude as individual fields. However, if you export a polygon or line dataset you will not have any geometry information.
This is due to Microsoft Excel not supporting Geometries as a type of field and the understanding that multi-vertex geometries can contain a lot of data. For example, the coastline of California can have thousands of point in one line, which would cause the data in that field to be huge.
If you want to export the geometries, please choose CSV and then import the CSV into Excel. The CSV will have the geometry stored as Well Known Text (WKT).