sort by update_time does not work for Get All Files

I am trying below endpoint to fetch files records.

https://api.pipedrive.com/v1/files?start=0&api_token={{api_token}}&limit=100&sort=update_time desc

According to this documentation, it allows to query the above endpoint with sort( id , update_time) parama. But, when I hit this endpoint with sort=update_time, it returns empty list.

Also, I have observed that sort with other fields like add_time works even though it is not mentioned in the API documenation.

Is this there some issue from API endpoint side? Does it really allow to query based on update_time? Can someone please clarify?