The installation process began, and John was prompted to select the language and agree to the terms and conditions. He chose his preferred language and clicked "Continue." The installer then asked him to select the disk where he wanted to install the operating system. John selected his main hard drive and clicked "Install."

date 0101010118

Boot and install 6. Plug USB into the target Mac and restart while holding Option (Alt) key. 7. Select the USB installer and press Enter. 8. (Optional) Use Disk Utility from the installer to erase/format the target drive as APFS (recommended for SSDs) or Mac OS Extended (Journaled) for older setups. GUID Partition Map must be used. 9. Choose "Install macOS" and follow on-screen instructions.

Let me know if you meant:

hdiutil attach /tmp/HighSierra.dmg -noverify -mountpoint /Volumes/macOS

Because Apple does not provide a direct .iso file for download, users typically must create one from the official installer application.