I wish Apple hadn't abandoned so many devices to rot on an old version for no good reason and then made their "One" service only work on the latest version as a blatant push to make people buy a new iDevice when the one they have would work just fine otherwise.
My old iPhone 7 (manufactured Sep 2016-2019) received a security update last month. Meanwhile, I bought a Samsung Android tablet new a few years ago only to find that the currently selling model wouldn't upgrade to the current very of Android.
I'm not an iPhone user, but they have better long-term updates than the vast majority of other vendors. Five years of support, I don't disagree with them wanting to push their newest device - they are a business and want to make money. Most features work except for things where there are hardware limitations.
Your example didn't really make any sense, as you can use Apple One on iOS 14 or newer. So the oldest supported iPhone would be the 6s from 2015, which at the point iOS 14 came out was already 5 years old.