how to store everything on iCloud not on mac

iCloud is primarily a syncing mechanism and not a cloud-only storage service. However, you can potentially reduce the storage used on the Mac by turning on the Optimize Storage option for photos (Photos app > Settings > iCloud > Optimize Mac Storage) and the Optimize storage option for iCloud Drive ( Apple menu > System Settings > [username] > iCloud > Optimize Mac Storage).

Also see: Set up and use iCloud Photos - Apple Support

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Set up iCloud on your Mac - Apple Support

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Store files in iCloud Drive on Mac - Apple Support

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Add your Desktop and Documents files to iCloud Drive - Apple Support