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Step-by-Step: Creating a Bootable USB for Clean Installation

Once installed, go to System Preferences > Software Update to get the latest security patches for 10.15. Step-by-Step: Creating a Bootable USB for Clean Installation

Now that you have a bootable installer, you can perform a clean installation of macOS 10.15 Catalina: macOS Catalina dmg file download for old macbook

Remember, to keep your Mac secure and your data safe, always obtain the installer from official sources, never from third-party websites, and always create a complete backup beforehand. never from third-party websites

If you are operating a compatible machine running macOS 10.15 or later, you can prompt the operating system to safely pull the original payload file directly through Apple infrastructure. macOS Catalina dmg file download for old macbook pro

Are you installing it on or a virtual machine ? What is the exact model year of the destination device?

Restart your Mac and immediately hold down Command (⌘) + R until you see the Apple logo.