softwareupdate --list-full-installers If High Sierra appears, download it with:
Use this direct URL: macappstores://apps.apple.com/app/id1246284741?mt=12 Open Terminal and enter: macos high sierra 10.13 iso download
softwareupdate --fetch-full-installer --full-installer-version 10.13.6 A Python script that downloads macOS installers directly from Apple’s servers without authentication: softwareupdate --list-full-installers If High Sierra appears