Are you certain that you have an iPad mini2 - and do not actually have an original first generation iPad mini?
Misidentification of an iPad mini1 as a mini2 (a.k.a. mini Retina) is not uncommon. You can verify your actual model from information in your iPad Settings:
Settings > General > About
A first generation iPad mini can only be updated to iOS 9.3.5 (WiFi Only models) or iOS 9.3.6 (WiFi & Cellular models).
Apple ended update support for iPad mini in September 2016. An iPad mini1 cannot be updated to iOS 10 or later major versions of iOS, as the internal hardware does not meet the minimum technical requirements for new versions of iOS/iPadOS. This limitation cannot be bypassed - in addition to which, iPad mini is a 32-bit architecture device, whilst all recent versions of iOS/iPadOS are designed for 64-bit hardware platforms.
iPad mini2 and mini3 are similarly limited to iOS 12.4.8. For these models of iPad, Apple ended major update support in September 2019. Since then, there have only been a few “point” security updates - the most recent being iOS 12.4.8.
iPad mini4 and the current mini5 (current) both support iPadOS 13.6.1, this being the current release.
You may wish to consider that compatible Apps for older iPad models are increasingly difficult to find - as third-party developers are increasingly dropping support for older versions of iOS preceding iOS11/12/13. As older versions of Apps are removed from the Apple App Store, you’ll not be able to (re)download or install them - which may severely limit the usefulness and utility of your iPad if you should you need to reset or restore your iPad - or if your iPad is ever disabled through repeated attempts to enter an incorrect passcode.
If you do in fact have an iPad mini1 and need access to most current Apps, requiring more recent versions of iOS than your iPad can support, you’ll need to consider replacement of your iPad with a newer or current model.
I hope this information is helpful is resolving the mystery as to why your are experiencing difficulties with updating your iPad mini.