Having full macOS installers is very useful if you want to create USB drives to use across several devices or if you just want to have offline access to macOS updates for other purposes.
Downloading macOS updates from the Mac App Store will only get you a small installer file, and you will need to download the full installer package (over 8 GB) over the internet.
Once you’ve downloaded the full package, it will immediately launch to update your OS. There’s no straightforward way to download the installer onto your computer and then possibly install it on another machine.
If you want to acquire the full macOS Catalina 10.15 installer, you will need to use third-party software to get the full package.
- Go to this site: http://dosdude1.com/catalina/ and click on the Catalina patcher application to download.
- Upon the first launch of the application, your machine may not allow it to be opened. Go to System Preferences – Security and click Open Anyway.
- Launch the patcher and click Continue.
- Select Download a Copy and confirm.
Once you’ve downloaded the full installer package, you can mount it on a USB drive for installation on multiple Catalina-compatible Macs.