softwareupdate --fetch-full-installer --full-installer-version 10.15.7 GibMacOS Script : A popular cross-platform Python tool, gibMacOS on GitHub
: Apple provides manual downloads for Combo Updates (e.g., 10.15.7 Combo Update ), but these require an existing Catalina installation to run . 2. Create a DMG Image macOS Catalina - App Store download macos catalina 10.15 iso and dmg image