A: A DMG includes partition maps and checksum data. The InstallESD.dmg inside is the compressed system image.

Introduction: Why macOS Catalina Still Matters

sudo date 091212002019 Then run the installer. After success, re-enable auto-date. Requirement: 12.5GB free space on boot drive. Fix: Use Disk Utility > First Aid, then delete local Time Machine snapshots:

macappstores://apps.apple.com/us/app/macos-catalina/id1466841314?mt=12