Although High Sierra might not be directly available for purchase/download through the Mac App Store on newer macOS versions, you might find it through searching or under the "Purchased" tab if you've previously bought it.
: If you are using a newer Mac and need the file for a bootable installer, visit Apple's official support page for downloading older macOS versions Creating a Bootable Installer macos high sierra 1013 6 dmg cracked
: If you already have an earlier version of High Sierra, you can download the 10.13.6 Combo Update (approx. 2GB) directly from Apple Support . Although High Sierra might not be directly available