Special editions like the Windows Embedded 8.1 Industry Pro Evaluation may still be available as a 180-day trial.
Microsoft has largely phased out direct public ISO downloads for Windows 8.1, but some official avenues may still be accessible for licensed users: Windows 8.1 Pro March 2022 Free Download
If you already have a Windows 8.1 Pro product key, you can sometimes use the Microsoft Software Download page to create installation media. March 2022 Updates & ISOs Special editions like the Windows Embedded 8