Apr 12, 2020 Part 2. Download macOS Catalina From Mac App Store. Apple always recommends its users downloading macOS install file from Mac App Store for security reasons. It is safe and easy. But the actual downloaded file is not an dmg file. Instead, it is an app called Install macOS Catalina, which is used to make the upgrade from current macOS to. See full list on isoriver.com. Jan 10, 2020 S..