Once you have the "Install macOS High Sierra" app in your Applications folder, follow these steps to create a bootable drive:

Often, the most reliable place to find the full ~5GB installer, including the "Install macOS High Sierra.app," is the Internet Archive.

Choose the "Install macOS High Sierra" drive from the menu. Install: Select "Install macOS" from the utility window.

Use Apple’s built-in tool to populate the image with the setup files: sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/install_build Type your administrator password when prompted.