Issue
When creating a Excel Spreadsheet, using a Create List Item action, the Excel spreadsheet does not open, and shows the error:
"We are sorry, we could not open your workbook. It's possibly corrupt or using a file format that is not supported."
Resolution
This is an underlying issue with the Sharepoint platform and also occurs with a Sharepoint Designer Workflow action: "Create List Item"
As an alternative, use the O365 action “Office 365 Upload File"