Create thumbnail images or previews of common files and custom file types on earlier versions of macOS.
The QuickLook framework provides functionality to create a miniature representation, or thumbnail, of a file and its contents for display in apps that target macOS 10.14 and earlier.
If your app targets macOS 10.15 and later, use the QuickLookThumbnailing framework to create thumbnails. Similarly, use a Quick Look Preview extension to display previews of files instead of Quick Look generators. To learn more, watch What’s New in File Management and Quick Look.