ipad says ios 12.4.8 is up to date, unable to update to iOS 14

This is probably an iPad that is outdated and does not have the hardware that is needed to support any other versions of iOS or iPadOS. You didn't mention what model iPad you have but this is what you are going to see when an iPad is updated as far as the hardware will allow it to be updated. Unfortunately if this is the case, the only option that you have if you want updated software is to update your hardware by replacing it with a newer device.

I surmise that you have an original first generation iPad Air, an iPad mini2 or mini3. These models of iPad can only be updated to iOS 12.4.8.

Apple ended update support for these devices in September 2019. Whilst they have received security “point” updates over the last year, they cannot be updated to iPadOS 13 (or any later major versions of iPadOS) as the internal hardware does not meet the minimum technical requirements for new versions of iOS/iPadOS.

Some App developers have dropped support for iOS versions preceding iOS 13.x for technical reasons (often because APIs or software libraries upon which they rely have been updated in the new version of iPadOS, making their App incompatible with earlier versions). 

Whilst many App titles remain compatible with your iPad, if you want or need to access to Apps requiring the most recent versions of iOS, you’ll need to consider replacement of your iPad with a newer or current model that supports iPadOS14.

I hope this information provides helpful clarity as to your available options - and the limitations of your existing iPad.