If you need an older macOS version, consider:
As the installation bar crawled across the screen of his 2011 MacBook Pro—one of the last generations compatible with High Sierra—Elias felt the weight of the OS. High Sierra was the bridge between two worlds: macos high sierra 10.13.5.iso
Before seeking out the ISO, ensure your hardware can actually run High Sierra. Generally, if your Mac can run Sierra (10.12), it can run High Sierra. Late 2009 or newer MacBook Air/Pro: Late 2008 or newer iMac: Late 2009 or newer Mac mini: Mid 2010 or newer Mac Pro: Mid 2010 or newer How to Obtain and Use the ISO If you need an older macOS version, consider: