Big Sur is officially supported by 2013 Mac models (8 years). iOS 15 is supported by the 6s, which was 2015. So 6 years. And I still know people using devices

Big Sur is officially supported by 2013 Mac models (8 years). iOS 15 is supported by the 6s, which was 2015. So 6 years. And I still know people using devices from these eras. Apple may not be repair friendly, but at the end of the day, their devices are the least likely to end up in the trash.