[danaris]

There is a huge difference between a ten-year-old laptop/desktop and a ten-year-old phone—or, more accurately, laptops and desktops have advanced a lot less in the past ten years than phones have.

It would be a much better analogy if you were to say you'd installed the latest Ubuntu on a machine from twenty years ago (though even that may be generous, given that the iPhone was only 4 years old 10 years ago, while the Intel PC was roughly 20 years old 20 years ago)—and I'd expect it to work about as well as iOS 15 would on an iPhone 4.

[mmastrac]

Or maybe installing the latest upcoming version of OSX on a mid-2014 Macbook Pro, which if I'm not mistaken, will not work.

[iSnow]

It'll work if you install a piece of software that changes the device identifier.

You are right though that Apple retires support after 6-7y. That surely could be longer considering how desktop/mobile CPUs have stagnated over the last 5-10y.

It's just unlikely to change given Apple makes no money supporting old computers apart from repairs.