The oldest Macs that support Sierra (10.12) or High Sierra (10.13) are from 2009. You may be able to bypass these restrictions which are often based on graphics

The oldest Macs that support Sierra (10.12) or High Sierra (10.13) are from 2009. You may be able to bypass these restrictions which are often based on graphics chips through kernel extensions, but discontinued support for 32bit probably has much more to do with older software than older hardware. If you want to find unusual problems with older Apple hardware for the sake of reusability, take a look at the firmware from around that time. It was just weird enough to make it similar to standards but often too difficult to support a decade later. In a decade, people are going to say the same about the not-quite NVMe SSD interfaces in current Macs.