When Microsoft first announced Windows 11, they unveiled some of the minimum hardware requirements you would need in order to upgrade to it. One of those requirements is a CPU introduced after 2017, so for those with older computers, it would seem like you might be out of luck. However, Microsoft did state that they were considering lowering the requirements, and the good news is that they have, sort of.

Link: Microsoft Changes CPU Requirements For Windows 11
via http://www.ubergizmo.com