: Follow the on-screen instructions. This will not install the OS yet; it extracts the "Install macOS Sierra" app into your Applications folder.
You can download the disk image (.dmg) file directly from Apple's official support channels . This version is the final release for the Sierra operating system and is compatible with various Mac models from late 2009 to mid-2010 or newer. Official Download Links Mac Os Sierra 10.12.6 Dmg File Download
Short checklist before proceeding
Remember: always avoid shady download sites, double-check checksums, and keep a backup of the DMG on an external drive for future use. Whether you’re reviving a 2010 MacBook Pro for a child’s first computer or running music production software that never got a modern update, Sierra 10.12.6 remains a rock-solid choice. : Follow the on-screen instructions