You must download the installer on a different Mac that is running an older OS (like High Sierra or Mojave) and copy the "Install macOS Sierra.app" to your target Mac via a USB drive or network transfer.
Before you begin, ensure you meet these requirements: macos sierra 10.12.6 download
: Apple maintains a support page for downloading older macOS versions if the App Store is unavailable on your device. YouTube +5 Hardware Compatibility & Requirements macOS Sierra dropped support for several older Mac models. To install version 10.12.6, your Mac must meet the following hardware criteria: Wikipedia +2 Mac Model Minimum Year Requirement MacBook Late 2009 or newer MacBook Pro Mid 2010 or newer MacBook Air Late 2010 or newer Mac mini Mid 2010 or newer iMac Late 2009 or newer Mac Pro Mid 2010 or newer Technical Prerequisites: 10 sites Create a Bootable USB Flash Drive for macOS Sierra (Step by ... 24 Nov 2016 — You must download the installer on a different
A stable, lightweight final release for 2010–2016 Macs. Only download if you need 32-bit app support or are stuck on older hardware. Avoid for security or modern features. To install version 10