I have an iPad Air model MD785LL/B how do I get the newest update I cannot get any new versions, version 12.4.8

You have a first generation iPad Air.

The original “first generation” iPad Air cannot be updated to iPadOS 13.x as it lacks the necessary minimum CPU and RAM specification to support newer version of the Operating System.

Update Support for iPad Air ended in September 2019 - the final supported version of iOS being iOS 12.4.8. As such, your description implies that you have already updated to the most recent version of iOS supported by your iPad.

If Apps that you need require iPadOS13 or later, then you have no alternative other than to replace your iPad with a newer model.

Sorry, this is perhaps not the news that you were hoping to hear, but I hope this information is helpful in informing your options.

If you want to use newest iOS/iPadOS versions, yes.

Your iPad model, because of hardware incompatibility, cannot support iOS versions beyond 12.4.8.

Regards

Giulio