Immediately after announcing that GnollHack requires Windows 11, people started sending reports that it works on their Windows 10 devices. Therefore, we decreased the minimum required operating system version back to Windows 10. However, we started a thread for collecting working and not working version numbers here:
https://steamcommunity.com/app/3558190/discussions/0/601904795201096250/
You may post there reports how the game works for you, if you have Windows 10.