softwareupdate --fetch-full-installer --full-installer-version 10.15.7
For users who need a specific version of Catalina or prefer working from the command line, Apple provides a way to download installers using the softwareupdate command.
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MyUSB
softwareupdate --fetch-full-installer --full-installer-version 10.15.7
For users who need a specific version of Catalina or prefer working from the command line, Apple provides a way to download installers using the softwareupdate command. Download Macos 10.15 Catalina Dmg File
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MyUSB Download Macos 10.15 Catalina Dmg File