Why is my iPhone (or iPad) not supported by apps, iOS?
In simplest terms, this is a trade-off with features, costs, performance, and the numbers of users using the older iPhone and iPad models, versus the numbers of those using newer.
Though the specific details here will differ, this applies across all older iPhone and iPad models, and across iOS and iPadOS versions.
For the purposes of this discussion, assume an iPhone 7.
When compared against 2018-era iPhone models, the 2016-era iPhone 7 has comparatively low performance, and is lacking hardware features used with newer iOS.
How to characterize that?
iPhone 7 with the Apple A10 processor provides two performance processor cores and two efficiency processor cores, with 2 GB of memory.
In a common processor benchmark, performance of the iPhone 7 is ~757 for single-core, and ~967 for multi-core performance.
For comparison purposes, the oldest iPhone models with support in iOS 17 and iOS 18 include the 2018-era iPhone XS and iPhone XR models.
These two iPhone models both use the Apple A12 processor, with two performance cores and four efficiency cores, with 4 GB of memory.
In the same performance benchmark, these provide ~1300 for single-core performance, and ~2234 for multi-core performance.
Put differently, iPhone 7 has half the memory, and has half the single-core performance of some of the oldest iPhones supported with iOS 17 and iOS 18. And has a processor lacking in hardware features that newer iOS and newer apps can expect or need.
The choice for Apple here being the extra effort needed to maintain the performance and capabilities of an older design, or of hobbling parts of iOS either on that design or hobbling it more generally for newer users and newer devices, or quite probably a combination of those approaches. Or dropping the older devices and more fully using the available features and capabilities of the newer processors in iOS for the newer iPhones.
Supporting and testing and providing work-arounds for older devices is not without associated cost too, and those older devices just aren’t going to get iOS and app features requiring newer hardware. Bug fixes and security patches need to work across all supported versions and models too, which means each new different configuration adds costs, time, and testing.
For third-party app vendors, they too have decisions and tradeoffs to make around support and related costs. Supporting older versions is far from free. Apps can often require different app code for newer features, for instance. New iOS or iPadOS features that the vendor may want to adopt. This means the app vendor has to pick either different versions for older devices, or different code within the same app and different testing. Or dropping the oldest versions, particularly if the app vendor has fewer users of those older devices. In any of these cases, this all adds cost and complexity for the app vendors.
For a write-up provided by Apple on this topic: Longevity, by Design (June 2024)