This is the official command-line tool provided by Apple. It creates a valid installer but typically requires running via Terminal (instructions included below) as Apple no longer provides a standalone .dmg for direct double-click installation.
Users search for "macOS Big Sur 1121" because they either: macos big sur 1121 installer dmg
Obtaining a macOS Big Sur 11.2.1 installer DMG is typically done for creating bootable USB drives or for use in virtual machines. This specific version, released in February 2021, addressed critical charging issues for some MacBook Pro models and included important security fixes [1, 2]. Methods to Obtain the Installer Official Mac App Store : The most secure way to get macOS Big Sur is through the Mac App Store . While it usually downloads the version of Big Sur, it is the safest starting point [3]. Terminal (Mist/SoftwareUpdate) : Advanced users can use the softwareupdate This is the official command-line tool provided by Apple