In June 2014, Apple announced that development of Aperture has been discontinued. Since then, Apple has released six major macOS upgrades. For technical reasons, macOS Mojave is the last version of macOS to run Aperture. Starting with macOS Catalina, Aperture is no longer compatible with macOS.

To continue working with your Aperture photo libraries, you must migrate them to another photo app. You can migrate them to the Photos app, which is included with macOS Yosemite or later, or migrate them to Adobe Lightroom Classic or another app. You should do this before upgrading to macOS Catalina.