Ensure that you selected GUID Partition Map when formatting the USB drive. Legacy MBR partition maps will not boot on modern Intel Macs.
Compare the output against known official Apple hashes. For the DMG specifically, a known MD5 hash for the Catalina 10.15.7 (19H15) full installer is: 97C28BCC7EAA7682E2D8C496ADC5EE85 . download macos catalina 10157 dmg file install
If you are already on a newer macOS, it might try to open Software Update. Click 2. Download via Apple Support (Update DMGs) Ensure that you selected GUID Partition Map when
A voice emanated from the speakers. It wasn't Siri. It was synthesized, yet warm. "You download macos catalina 10157 dmg file install
: Follow the on-screen instructions to extract the installer into your Applications folder.