
Hi MrMathews,
Thank you for posting on Microsoft Community!
I tested this on my mobile device (iOS) and confirm that when I access an Excel file through the Outlook app and then tap to open the file in the Excel mobile app, the file is not downloaded to my device. Instead, it opens for editing or viewing. Due to this, the action does not appear as a download in the audit log.
In addition, you can read more information about audit log at: Audit log activities | Microsoft Learn
If you need any further assistance, please feel free to ask!
Sincerely,
Nam-D - MSFT | Microsoft Community Support Specialist