Submissions from multiple webforms in one csv export

Problem/Motivation

We have some webforms used for recording interviews and we need to export the submissions results from all webforms in one csv file.

1. We have tried to use the webform_views and views_data_export modules. We have been able to create a view combining all the results, exactly as needed. When creating a 'Page' display, we have a 'Webform Submission' option in the 'Format' section, as per the screenshot attached. When we attempt to create a 'Data Export' display, this option is unavailable. There is an 'Entity' option, but this does not have the webform fields, only some general things such as IP, etc.
2. We have also looked at extending the WebformSubmissionExporter.php class to pass through the submissions we require. We found it challenging to make this work with more than one webform.