down load and install os 11

Hi Daniel,

The current version of macOS is macOS Monterey 12.0.1. To install that version (if your Mac is compatible), search for macOS Monterey in the App Store.

If you still want to install macOS Big Sur instead, you can do so using this link: How to get old versions of macOS - Apple Support

However, before you install any upgrade, we need to know when your MacBook Air was made. This determines whether it is even compatible with the newer versions of macOS.

See this page for the macOS11 Big Sur installer you wanted: How to get old versions of macOS – Apple Support (UK)

Make sure your device is compatible with the OS which is also included on the same page.