can i upgrade my mackbook air it has high sierra 10.12.6

The model year of a MacBook Air is available at Apple menu > About This Mac.

A late 2010 through mid 2011 MacBook Air can be upgraded to High Sierra 10.13.6 but no later version. See: How to get old versions of macOS - Apple Support

A mid 2012 MacBook Air can be upgraded to Catalina 10.15.7 but no later. See: How to get old versions of macOS - Apple Support

A mid 2013 and early 2014 can be upgraded to the latest version of Big Sur macOS 11 but no later. See: How to get old versions of macOS - Apple Support

An early 2015 or later can be upgraded to the current version of Monterey macOS 12. See: How to upgrade to macOS Monterey - Apple Support

If you mean Sierra(10.12), you can upgrade it to High Sierra(10.13). Any newer OS version requires it to be at least a 2012 model.

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