Even if you updated when iOS 12 was still receiving updates, the latest you can update to is iOS 12.4.1 while iOS 12.4.2 and later were only for iPhone 5s and iPhone 6s [limiting the discussion to iPhones only]
Exactly, which makes, like I said, longer-term security updates irrelevant. Even if Apple guaranteed 10 years of updates, they’d never allow you to install the latest security update for the current major iOS version.
I guess they could do that and only sign OTA releases, I don’t know whether that’s possible, but they have exactly zero interest in encouraging anyone to stay behind, as evidenced by their uncrackable, decades-old resolve to disallow downgrading.
I’ve never understood the logic behind that, because even if it were security, you could just release security updates for, say, every iOS device on every iOS version until they’re officially classified as obsolete, and by then you could let users pretty much install whatever they want.
Since they have to know that iOS updates impact performance and battery life, if they really cared about long-term software quality they wouldn’t keep deprecating older iOS versions.
Developers and their pathetic obsession with dropping support for older iOS versions as fast as possible doesn’t help either.
The iPhone 11 on iOS 18 has worse performance (not too bad, but I’ve found some lag), when compared to iOS 14 and 15, but battery life is still-like new. I updated one from iOS 14 to iOS 18 and found no difference - in fact, iOS 18 was slightly better.
iOS 26 and its Liquid Glass makeover will possibly end that, however.