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Step 1: Securely Downloading the macOS High Sierra 10.13.6 DMG

The USB was not created correctly.

Step 1: Download the Official macOS High Sierra 10.13.6 Installer

Click the link to open in the Mac App Store.

This is typically a language or localization file issue.

Unlike modern macOS installers (which are .app bundles), High Sierra installers often circulated as .dmg files containing the Install macOS High Sierra.app . People sought these DMGs for:

MacBook (Late 2009 or newer) MacBook Pro (Mid 2010 or newer) MacBook Air (Late 2010 or newer) Mac mini (Mid 2010 or newer) iMac (Late 2009 or newer) Mac Pro (Mid 2010 or newer)