
What is the version of your office client application?
AutoSave is a new feature available in Excel, Word, and PowerPoint for Microsoft 365 subscribers that saves your file automatically, every few seconds, as you work.
AutoSave is enabled when working on a file that is saved to OneDrive, OneDrive for Business, or SharePoint Online. If the file is saved to another location (or if it hasn't been saved at all, yet), then AutoSave is disabled. This will happen if your file is on a SharePoint on premises site, a file server, some other cloud storage service, or saved to a local path like C.
Reference: https://support.microsoft.com/en-us/office/what-is-autosave-6d6bd723-ebfd-4e40-b5f6-ae6e8088f7a5
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