Information
This policy setting controls the default file format for saving workbooks in Excel.
The recommended state for this setting is: Enabled: Excel Workbook (*.xlsx)
If a new Excel file is created in an earlier format, some users may not be unable to open or use the file, or they may choose a format that is less secure than the default format.
Solution
To establish the recommended state via configuration profiles, set the following Settings Catalog path to Enabled: Excel Workbook (*.xlsx) :
Microsoft Excel 2016\Excel Options\Save\Default File Format
Impact:
Enabling this setting does not prevent users from choosing a different file format for a new Excel file, and therefore, it is unlikely to affect usability for most users.