iPad old version of iOS risks

The first generation iPad Air, iPad mini2 and mini3 can only be updated to iOS 12.5.7. 

Apple ended major update support for these models of iPad in September 2019 - although they have since continued to receive occasional “point” security updates - the most recent being released in January 2023. As you are perhaps aware, these devices 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.

Due to the system architecture of iOS/iPadOS, unless jailbroken, your iPad is not susceptible to traditional malware infection per-se. However, as with all computer systems, there are still vulnerabilities and exploits to which you remain vulnerable. For older devices, no longer benefiting from regular security updates, the risk of an unpatched vulnerability being exploited significantly increases.  Older devices, with unpatched vulnerabilities, are actively targeted by threat Actors.

Given that your device is well within its twilight period of update support, if ever used online - and especially if used to access financial or e-commerce Apps or services, you would be well advised to consider replacement with a more recent device - in so doing benefiting from both enhanced functionality, regular security updates and full update support. Of current models, even the entry-level iPad9 has specifications and capabilities that will massively outperform you current iPad - and is compatible with iPadOS16 and the vast majority of current Apps. Other models are more powerful still.

Many banks and other finance-related websites and financial services will require that up-to-date Operating Systems and browser software are used to access and maintain accounts. Financial fraud and theft is a major concern. Continuing to use older/obsolete hardware considerably increases the risk of device and/or account compromise.

if it was me then I would not worry too much, since we can't install software of any sort from other sources than app store then, any unfixed wounability the older device could have to require the want to be hacker to target your device directly