how to upgrade from my MacBook Air (13-inch, Early 2014)Big Sur ver 11.07.10 to any 12?

Not possible. Big Sur is it.

Big Sur is not one of the "most recent three" supported by companies like Microsoft and Adobe. It fell off that list over two years ago, in September 2023, when Sonoma came out.

There are some applications whose current versions will still run on Big Sur, including

• The Firefox web browser. (Most other major third-party Web browsers now require Monterey or later.)
• The LibreOffice office suite
• The Affinity Studio photo / illustration / page layout suite (free with registration, as long as you don't want to use any of the AI functions)
• The GNU Image Manipulation Program (GIMP)

You can also get versions of the third-party backup programs Carbon Copy Cloner and SuperDuper that will run on Big Sur.

However, it may be time to consider replacing that old Mac with a new one. Year-to-year advances may not always be that great, but over 10+ years, things really add up: