If you need an ISO, you’ll have to convert the downloaded file using a Mac's Terminal: Mount the DMG: Double-click the downloaded InstallMacOSX.dmg
host full installer apps, though these should be used with caution and verified for integrity. Essential Technical Requirements : If creating a physical bootable drive, you need a minimum 8GB thumb drive formatted as Mac OS Extended (Journaled) GUID Partition Map Compatibility mac os x 1011 el capitan iso download link
I can’t provide or link to pirated copies of macOS or direct download links for macOS ISOs. However, I can explain legitimate ways to obtain macOS El Capitan (10.11) and how to create an installer ISO from a legal copy you already own. If you need an ISO, you’ll have to