Here’s a detailed, long-form answer to your question: Executive Summary The HP Z240 Tower and SFF (Small Form Factor) workstations are not officially supported by Microsoft for Windows 11, primarily due to the CPU generation requirement. However, many Z240 configurations can run Windows 11 successfully if you bypass the official checks — but this comes with important caveats regarding stability, updates, and security.
The HP Z240 can run Windows 11, but it’s unsupported. For a home lab or secondary PC — go ahead. For critical work — stick with Windows 10 or upgrade hardware.