sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MyUSB
softwareupdate --fetch-full-installer --full-installer-version 10.15.7 Macos Catalina Dmg Direct Download
c2cf9fa2ed6a500bfcbbd385e1d8b16aebfb0fbc sudo /Applications/Install\ macOS\ Catalina
gibMacOS is a popular, open-source script that allows you to download macOS installers directly from Apple's software update catalogs on both Windows and Mac. Macos Catalina Dmg Direct Download
If you are on a Mac running macOS 10.15 or later, you can bypass the App Store and use the Terminal to download the full installer: