In this guide, we’ll cover why you might need the DMG file and the safest ways to get it. Why Download the macOS Catalina DMG?
A valid, unmodified installer will show output indicating it was signed by "Developer ID Installer: Apple Inc." and will not display any errors. You can also perform an SHA-256 checksum to compare against a known good value, though the code signature verification is typically sufficient for ensuring authenticity. Mac Os Catalina 10.15 7 Dmg Download