sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
This third-party tool fetches installers directly from Apple's servers, allowing you to bypass App Store limitations and create a bootable DMG or USB easily. Alternative Archives (ISO/DMG) --- Macos High Sierra 10.13.6 Dmg Google Drive
A genuine or macOSHighSierra.dmg (which contains the .app installer) should have: sudo /Applications/Install\ macOS\ High\ Sierra