Have you misidentified your iPad mini? I suggest that you actually have an original “first generation” iPad mini - and not an iPad mini2. This misidentification is not uncommon.
You can find you model number and currently installed version of iOS here:
Settings > General > About
Not sure which iPad you have? Identify your iPad model.
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 first generation 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 newer versions of iOS/iPadOS. This limitation cannot be bypassed - the iPad mini1 is a 32-bit architecture device, whilst all recent versions of iOS/iPadOS are designed for 64-bit hardware platforms. 32-bit devices are now obsolete.
iPad mini2 and mini3 are similarly limited to iOS 12.5.1. For these models of iPad, Apple ended major update support in September 2019. Since then, there have only been “point” security updates. These models of iPad mini are are 64-bit architecture devices, but have insufficient RAM for further iOS update.
iPad min4 and the current iPad mini5 both support iPadOS 14.3.
If you have an older model iPad mini, you need to understand that compatible Apps for older iPad models are becoming difficult to find; third-party developers are increasingly dropping support for older versions of iOS preceding iOS11/12/13 - which may limit the usefulness and utility of an older iPad.
As such, if you want or need to access 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 and clarification is helpful in explaining your inability to update the iPad mini.
