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Cloud Filter Functions don't expose the Automatic file downloads notification option, which is controlled by Automatic file downloads application and as Build a Cloud Sync Engine that Supports Placeholder Files said, Users are always in control of file hydration, even when the files are not hydrated explicitly by the user. An interactive toast is shown for background hydration to alert the user and provide options.
To disable Automatic file downloads notification, Select the Start button, then select Settings > System > Notifications & actions, and then under Get notifications from these senders turn off Automatic file downloads.
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