codesign -dv --verbose=4 /path/to/InstallESD.dmg

Use to format it as Mac OS Extended (Journaled) with a GUID Partition Map .

The official App Store download provides an .app file, not a .dmg . If you specifically need a DMG (e.g., for virtual machines or bootable media), you can create one from the verified .app file:

Click or Download . The installer will download to your /Applications folder as "Install macOS High Sierra.app".

Download macOS High Sierra 10.13.6 Combo Update - Apple Support

To check a DMG you already have:

Look for uploads from verified users like “Mr. Macintosh” or “dosdude1” (famous for legacy patchers). Download the file, then .

If your current Mac is running a significantly newer OS (like macOS Ventura or Sonoma), the App Store may block the download, stating the OS is "too old" for your machine. In this case, you will need to use the Terminal method. The Professional Method: Terminal Commands