App updates will continue to be available as long as the apps are supporting the iOS version that you have. At some point the app developers might drop support for older iOS versions—some might do it faster than others and others still might not do it at all or not for a very long time. With iOS 12 there’s still some time to go before even some will stop putting out updates that support it.Hello
I have an iPhone 5, and I think 12.4.3 is going to be the last update, so until when the iPhone is going to receive apps updates?
The other thing to be aware of is that it's not uncommon when new apps are introduced that they require the current iOS version, and don't necessarily support earlier versions. I've had this happen a few times over the years.
Similarly, new versions of an app may require the latest iOS version to support new features because the underlying functionality is in the latest iOS version.
None of this is fatal but it can be annoying.
What about security? for example Paypal app