I have no idea why it's not supported. It is an old unit, (3Q/2015) I have a i7-6700K (2 desktops) also (3Q/2015). Purchased 2017, I loaded Win 11 from scratch and re-installed all my apps and they work fine. Patches also worked. My opinion is either MS or Dell which I use want you to buy new equipment. The CPUs have not failed so far. My opinion may be wrong, but i doubt it. Just a money-making scam. I am going to try VMWARE and then run Win11. I'll wait to 2025 to upgrade if I need to. May not need a PC then, probably will be able to run anything from my I-pad or I-phone by then. (I am retired anyway)
Good luck.