Remember: the safest download is always from Apple. Avoid third-party “free DMG” websites at all costs. Use the App Store, Apple’s support page, or the softwareupdate terminal command. Once you have the genuine file, you can create a bootable USB, extract the InstallESD.dmg , or archive it for future restores.
When the download finishes, the file "Install macOS Catalina" will be in your Applications Method 2: Official Apple Support Downloads (Updates Only) mac os catalina 1015 7 dmg download free