Why can’t I update my iPad mini 2?

That model can't support iOS versions beyond 12.4.7 because of hardware incompatibility.

Regards

Giulio

If you are asking about updating iPad Mini 2 to iPadOS 13, it is not capable of going beyond iOS 12..x.x. It lacks the RAM required.

Another member may post a treatise on this, the reality is your device is now no longer supported and if you want the latest iPadOS, you'll need a newer device.