The Intel Core i7-5820K is a processor that was released in Q4 of 2014, as part of Intel's Haswell-E series. Windows 11, which was released in June 2021, has a minimum hardware requirement of processors from the 7th generation (Kaby Lake) or later.
Because the i7-5820K is a Haswell-E series processor, which part of the 4th generation processors, it does not meet the minimum requirements for running Windows 11. It means the i7-5820K can only support up to Windows 10.
It's important to note that this is not only a Windows 11 problem, but this would also apply to other operating systems that have similar minimum requirements. As technology advances, newer operating systems and software are designed to take advantage of the capabilities of newer hardware, which may not be compatible with older devices.
Additionally, Microsoft has a policy that they only support the most recent version of Windows on devices and processors that were manufactured after the most recent version of Windows was released. So any devices which manufactured during the release of Window 10, it may not support latest Window 11.
It's worth noting that, In some cases, hardware manufacturers may provide updates to make their hardware compatible with newer operating systems, but in this case as the i7-5820K is pretty old, it may not be possible to get any compatibility patch for it.
