Mac OS X El Capitan (version 10.11.6) is available as a free download from Apple for compatible older Mac models. The 10.11.6 version was the final release of El Capitan, issued on July 9, 2018, to improve stability, security, and compatibility. Official Download Methods
To install OS X 10.11.6, your Mac must meet these minimum specifications: OS X El Capitan - Technical Specifications - Apple Support Mac OS X El Capitan 10.11.6 Free Download
You can obtain the installer directly from Apple through these official channels: Mac OS X El Capitan (version 10
: If you already have an earlier version of El Capitan installed, you can download the 10.11.6 Combo Update (1.5 GB) to update your system directly. System Requirements System Requirements : While hidden from standard searches,
: While hidden from standard searches, you can still access the OS X El Capitan page on the Mac App Store via direct links.