softwareupdate --fetch-full-installer --full-installer-version 10.15.7 Use code with caution.
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/USB_DRIVE_NAME macos catalina download dmg
This guide covers how to officially obtain the installer, verify if your Mac is compatible, and create a bootable DMG for your needs. 1. Official Ways to Download macOS Catalina verify if your Mac is compatible