i want to update to ios 13

Perhaps your iPad Mini model cannot support iPadOS 13 or later, because of hardware incompatibility. See this support article:--> Identify your iPad model - Apple Support

These are the iPad models which can support iPadOS 13 or later:

The above list lacks of iPad Air 4th generation, just released.

Regards

Giulio

An iPad mini2 can only be updated to iOS 12.4.8.

Apple ended update support for iPad mini2 in September 2019. The mini2 cannot be updated to iPadOS 13 (or any later major versions of iPadOS) as the internal hardware does not meet the minimum technical requirements (CPU and RAM) for newer 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 mini2, 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.

Sorry, I appreciate that this may not be what you were hoping to learn.

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