This is the safest way to get the "Install macOS Catalina" application, which you can then use to create your own DMG or bootable USB.
The full installer will download directly into your folder. 3. Third-Party Tools and Scripts Download Macos 10.15 Catalina Dmg File
Open Terminal and type: softwareupdate --fetch-full-installer --full-installer-version 10.15.7 This is the safest way to get the
Practical Approaches to Obtain Catalina
If you have the installer app and need to convert it into a bootable DMG, follow these steps in Terminal: Create a blank image Download Macos 10.15 Catalina Dmg File