You can either download it from the Mac App Store or click here for direct download.
The latest version is 4.3.0 and supports macOS 10.7 or later. Don’t worry, it is easy and quick to do even it gets an error cannot open a file as an archive sometimes. 7z archive files regardless of what version of Mac OS you are using. Keep on reading as we are going to walk you through the steps for opening. 7-Zip Download (macOS) A Walkthrough on 7-Zip for Mac