Show you the command to turn your El Capitan ISO into a bootable USB.

This installer will unpack the official directly into your Mac's Applications folder. Method 2: Creating an ISO from the Official Installer

The system will download Install OS X El Capitan.app directly into your folder. How to Create an OS X El Capitan ISO File

How to obtain an El Capitan 10.11.6 .ISO … - Apple Community

OS X El Capitan 10.11.6: Features, Performance, and How to Securely Download the Installer

Open your web browser and navigate to the official website.

OS X El Capitan (version 10.11.6) is the final stable update of the twelfth major release of macOS, prioritizing performance, stability, and security. It is particularly valuable for users seeking to revive older Mac hardware or ensure compatibility with legacy software.

Download the official DMG from the link above.