Programmed software obsolescence is the acceleration of a device’s aging by updating its operating system. It’s ugly, and it’s extremely pernicious.
If your iPhone is compatible with iOS 14 (iPhone 6s and above), you will not have any compatibility issue with apps from the App Store. If your iPhone is compatible with iOS 12 or higher (so iPhone 5S and above), you should be fine for most apps.
If you want to make sure what apps work on your iPhone, take a look at this page. You can select at the top of the page your device, your iOS version and the type of apps you want to check.
To make it short, here is what you can’t do with an iPhone 6 (iOS 12), for instance:
- Some social networking apps won’t work anymore (like Tumblr).
- Some business apps won’t work either (like Outlook, ParkMobile or Scanner App).
- Same for some entertainment apps (like SoundCloud or Audible).
As far as games are concerned, you should be fine.
And to help you see things more clearly, here’s a list of supported iOS versions for each iPhone :
- iPhone 11, 11 Pro and 11 Pro Max: iOS 14
- iPhone XS MAX: iOS 14
- iPhone XS: iOS 14
- iPhone XR: iOS 14
- iPhone X: iOS 14
- iPhone 8 and 8 Plus: iOS 14
- iPhone 7 and 7 Plus: iOS 14
- iPhone SE: iOS 14
- iPhone 6S and 6S Plus: iOS 14
- iPhone 6 and 6 Plus : iOS 12.4
- iPhone 5S : iOS 12.4
- iPhone 5C : iOS 10.3.3
- iPhone 5 : iOS 10.3.3
- iPhone 4S : iOS 9.3.5
- iPhone 4 : iOS 7.1.2