This is the safest primary source. Use a web browser (preferably Safari) to download the file for El Capitan 10.11. Apple Support - Combo Updates
Last updated: 2025. Information accurate as of this writing. Mac Os X 10.11 El Capitan Iso Download
While Apple no longer directly offers Mac OS X 10.11 El Capitan for download, you can still obtain it through the Mac App Store or by creating an ISO file. When dealing with older operating systems, ensure you follow best practices for installation and maintain awareness of potential security risks. This is the safest primary source
hdiutil create -ov -format UDRW -volname "El Capitan" -size 6.5g ElCapitan.dmg Mac Os X 10.11 El Capitan Iso Download
If you doubt the source, test the ISO in a virtual machine before installing it on your primary hardware. Key Features of OS X 10.11