Ensure the file is sitting in your Applications folder.
Once finished, the installer application will appear inside your Applications folder named “Install macOS High Sierra.app” .
Example createinstallmedia command (after downloading the installer): Download Mac Os High Sierra 10.13.6 Dmg
The official download provides a .app file wrapper rather than a raw .dmg disk image. If you specifically require a file for archiving or virtual machines, you can create one manually using Terminal. Step-by-Step DMG Creation Open Terminal .
If you need help with any of these steps, please let me know: What is the target Mac? Do you plan to do an in-place upgrade or a clean install ? Are you installing on a physical Mac or a virtual machine ? Ensure the file is sitting in your Applications folder
Apple Footer * Support. * Download macOS High Sierra 10.13.6 Combo Update. Apple Support
You can find pre-made .dmg files on sites like archive.org or mrmacintosh.com . No checksum verification, possible malware, outdated versions. If you specifically require a file for archiving
sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled Use code with caution. Press and type your password. Press Y to confirm that you want to erase the volume.