Here is the first hurdle. ISO files are standard for Windows, Linux, and optical discs. Macs boot from .dmg or .cdr files.
Double-click the InstallMacOSX.dmg you downloaded.
Visit the Apple Support website and look for the "How to download macOS" page. They provide a direct link to the OS X El Capitan installer.
Mac OS X 10.11 El Capitan : Apple. Inc : Free Download, Borrow, and Streaming : Internet Archive. Internet Archive How to Download OS X El Capitan 10.11 (DMG, ISO, APP) Aug 29, 2568 BE —
Downloading and Installing Mac OS X El Capitan 10.11.6: A Complete 2026 Guide
