If you archive a client in Xero Practice Manager, this will archive the client and their documents in FYI. Refer to Archived Clients.
For active clients, there is currently no way to archive documents. However, this has been added to our feature request list.
Refer also to Bulk Export OneDrive.
Note: If you are part of the Beta release for Bulk Export AWS S3, you can also export to a designated AWS S3 directory. Refer to Bulk Export - Beta (this help article is only available to Beta sites).