The first and second generation Pencil use an entirely different pairing and charging interface. The second generation Pencil can only be used with iPad models that have the magnetic/inductive dock that is exclusively designed for the Pencil.
The first generation Apple Pencil, compatible with your iPad6, uses the physical Lightning port for both pairing and charging the first generation Pencil. This pencil can only be used with compatible iPad models that have a Lightning connector.
In summary, the Apple Pencil models are not interchangeable - and can only be used with the iPad that has appropriate internal hardware. A software update, should there ever be one, cannot add or modify the internal hardware.
Here is the definitive compatibility list for Apple Pencil and iPad:
Apple Pencil (2nd generation)
You can use Apple Pencil (2nd generation) with these iPad models:
- iPad Air (4th generation)
- iPad Pro 12.9-inch (3rd generation) and later
- iPad Pro 11-inch (1st generation) and later
Apple Pencil (1st generation)
You can use Apple Pencil (1st generation) with these iPad models:
- iPad (8th generation)
- iPad mini (5th generation)
- iPad (7th generation)
- iPad (6th generation)
- iPad Air (3rd generation)
- iPad Pro 12.9-inch (1st or 2nd generation)
- iPad Pro 10.5-inch
- iPad Pro 9.7-inch
Not sure which iPad you have? Identify your iPad model.