Please read more here
https://www.xero.com/nz/accounting-software/store-files/
What is Files used for in Xero?Your Xero file library contains an Inbox and Contracts folder. You can add any additional folders you need. Upload files to the file library or email files directly to the Inbox folder, then attach them to individual transactions, items and emails in Xero. See which transactions your files are attached to.
https://central.xero.com/s/article/Manage-your-file-library
Control-C ONLY backs up files attached to a Financial Transaction in Xero, hence the name Attachments and not Files.