sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/Catalina --nointeraction

softwareupdate --fetch-full-installer --full-installer-version 10.15.7

The most secure way to obtain a macOS Catalina image is through official Apple channels. While Apple typically provides an "installer app" rather than a raw DMG, this app serves as the foundation for creating one. Microsoft Community Hub Mac App Store