We are planning to export logs to the CSV files on a regular basis by using PowerShell commands. However, by the default, the data has become blank when the user sets the scope of logs to the specific document library. (which locates under the hierarchy) I found the workaround that to output logs of the files saved in the document library by changing the target range to the upper site.

In addition, I got a response from the support team that there is no function available to output logs that the specified document library at the present. Therefore, I hope the feature will be improved to specify the particular document library as a scope and output Office 365 audit log freely. Thank you for your continued support.