Yeah,
This may never happen.
If your iPad Air states that your iPad is up to date at iOS 12.5.1, you actually have a 9.7 inch screen iPad Air 1st generation and NOT a 2019, 10.5 inch screen iPad Air 3.
The 2013 iPad Air 1, iPad Mini 2 and 2014 iPad Mini 3 cannot upgrade beyond any version of iOS 12, currently at iOS 12.5.1.
These iPad models have overall internal hardware that is too old, too underpowered and incapable of running all of the new, advanced and internal hardware resource intensive features of iPadOS.
Also, NO Apple Pencils work with such an old iPad.
Old iPad models lack the necessary internal screen hardware layer needed for an Apple Pencil to be recognised and to work/function.
Sorry.