When your Mac is low on storage, only space-saving versions of your photos are stored on your Mac.
To access files stored in iCloud, simply double-click the icon to download the file. Files stored in iCloud have a download icon (a cloud with an arrow pointing down). When your Mac is low on storage, only recently opened files are stored on your Mac. When storing files on iCloud, you can choose from one of three options: Storing your content on iCloud, Apple's cloud storage service, helps you save space on your computer while still having easy access to your files.
