ISO image of macOS Sierra 10.12. 6. Downloaded from: https://sysin.org/blog/macOS-Sierra/ Internet Archive macOS Sierra 10.12.6 - ISO : Apple - Internet Archive
To create a bootable USB drive, you'll need a USB drive with at least 8GB of free space. Here are the steps: mac os sierra 10.12 6 iso download
Once you have Install macOS Sierra.app (≈ 4.8 GB): ISO image of macOS Sierra 10