Obtain the macOS High Sierra app from the App Store.

A DMG file allows you to run High Sierra inside software like VMware, VirtualBox, or Parallels on newer machines. How to Download macOS High Sierra 10.13.6 DMG Safely

Run the .pkg file inside to install the "Install macOS High Sierra" app into your Applications folder. Create Bootable USB (Recommended): Plug in a 16GB+ USB drive. Open Terminal and use the createinstallmedia command:

If you have a compatible Mac, you can download the full installer from the App Store using the direct link provided in the How to download and install macOS - Apple Support guide. This downloads the Install macOS High Sierra.app to your Applications folder, which can then be converted into a DMG.

Access the macOS High Sierra App Store page using Safari. If the "Get" button is active, it will download the "Install macOS High Sierra" app to your Applications folder.

Follow the on-screen prompts to complete the process. Installation Guide for macOS High Sierra