10.12 Sierra — Download ((link))

While it is an older OS, Sierra introduced several "Continuity" features that remain central to the Apple ecosystem today: macOS Sierra - Technical Specifications - Apple Support

This is usually a server timeout. Pause and resume the download in the "Purchases" tab of the App Store (if visible), or simply re-click the link from the Apple Support page. 10.12 sierra download

Open the "Install macOS Sierra" app from your Applications folder to begin the upgrade. While it is an older OS, Sierra introduced

(Recommended for updating an existing 10.12 installation to the final version) 💻 System Compatibility While it is an older OS