If you are on Windows or need specific installer files for a virtual machine or Hackintosh, the gibMacOS script on GitHub is a community-standard tool. It downloads official files directly from Apple's servers , ensuring authenticity.
Note that Apple's direct DMG links are often "Combo Updates" rather than full installers. Use the Mac App Store if you are currently on a compatible Mac. System Requirements for macOS Catalina download macos catalina 10157 dmg google drive best