Note: macOS 10.12 Sierra is no longer supported by Apple and is considered obsolete. This post includes the necessary security warnings and workarounds.
Sierra doubled down on connecting your Mac to your iPhone and Apple Watch.
Backup Your Data: Before proceeding with any OS installation or upgrade, it's highly recommended to back up your Mac. Use Time Machine or any other backup solution you prefer.
Additionally, your Mac must have at least 2 GB of RAM and 8.8 GB of available storage (though a full download plus installation requires ~12 GB).
Surprisingly, Apple’s Content Delivery Network (CDN) still hosts the full Sierra installer. You can trigger the download using a legitimate Apple Software Update URL.
: Because it no longer receives security patches, it is vulnerable to newer threats. It is best used for running legacy software or on older hardware that cannot support newer versions like High Sierra (10.13) or Catalina (10.15). 4. System Upgrades
Double-click the .pkg file inside and follow the prompts. This will "install" the actual "Install macOS Sierra" app into your Applications folder.
For older versions like Sierra, Apple provides a direct web download rather than a standard App Store search result.