You would be amazed and the industrial world. There are tons of large and incredibly expensive special purposes machines that are operated by super antiquated PC architecture computers running geriatric operating systems, sometimes still even DOS or Windows 3.x.

Think industrial CNC mills and lathes, presses, pick-and-place machines, specialty lab testing equipment, electron microscopes, etc.

Process control, i.e. production line automation, is usually driven by dedicated PLCs. But the user interfaces connected to them are almost invariantly some old ruggedized panel mounted PC running Windows. An absurd number of them in my experience are still on 2000 or XP. NT4 is pretty easy to find, too.

Granted often these are not networked, and in cases where they are they’re not connected to the internet, or may even talk to other workstations via RS-485 serial (!) or some other gimcrack method that is unlikely to be a vector for modern malware.