Well there's your answer. The app developers have decided - rightly or wrongly - that environments of a certain age (or more likely Android version) do not meet

Well there's your answer. The app developers have decided - rightly or wrongly - that environments of a certain age (or more likely Android version) do not meet their security requirements. My bank app supports Android 9+ which is nearing 5 years old now I think, and it should still work on my Pixel XL :) That said, the phone is definitely usable - as a phone and probably for texts and many other apps. But if the 2-4 year lifespan of your banking app is the issue, maybe just use it on the desktop or through a browser instead of the dedicated app. As long as you can get a recent-ish browser installed on your phone, you might be able to use the web banking interface (not all banks have mobile-friendly versions, admittedly). And yes, I believe the official stance of Google with regards to updates is 2 years of updates followed by 2 more years of security-only updates. Other manufacturers may do less than that, which is one reason I get the Pixel phones.