You are not addressing Apple here.
You have signed up into an Apple supplied product customer/user to user technical support community
We are all, largely, just Apple product customers/users, just like you.
Upgrading your iPad Mini 3 to iPadOS is never going to happen.
Sorry.
Your iPad Mini 3 cannot upgrade/update beyond any version of iOS 12, currently at iOS 12.5.1
The 2013 iPad Air 1, iPad Mini 2 and 2014 iPad Mini 3 cannot upgrade beyond any version of iOS 12.
These iPad models have overall internal hardware that is too old, too underpowered and incapable of running all of the new, advanced and internal hardware resource intensive features of iPadOS.
Sorry.
Forget any banking app and try accessing the banking Website through a Web browser, instead.
Try using a different third party Web browser instead of the iOS Safrai Web browser.
Sometimes, using a third party iOS Web browser will get by the banking Websites’ security issues when trying to login into your banking accounts using something other than the actual iOS Safari Web browser.
Do a search of the iOS App Store for Web browsers.
Many third party Web browsers still support iOS 11 or 12 and later.
Best of Luck to You!