Restart your Mac while holding the Option (⌥) key to select the USB drive as your startup disk. 4. Third-Party Tools for "Raw" Files
You can still find High Sierra on the Mac App Store , though it is often hidden from search results. Clicking this direct link from a compatible Mac should trigger the download. Macos High Sierra 10.13.6 Raw Download
Once you have the "Install macOS High Sierra.app" in your Applications folder, follow these steps to create a bootable drive for a clean installation. Restart your Mac while holding the Option (⌥)
If you are already on a newer version of macOS, you can often "fetch" the full installer by pasting this into your Terminal : softwareupdate --fetch-full-installer --full-installer-version 10.13.6 Clicking this direct link from a compatible Mac
This guide provides everything you need to safely find the and create a bootable installer. 1. Official macOS High Sierra Download Links