And you can actually download Windows on ARM from Microsoft Insider Preview for Free. And run it on top of Parallels Desktop 16.
What you were possibly remembering was that Windows on ARM when it was first introduced only supported emulating x86 apps. Although x64 emulation is currently in preview.
https://docs.microsoft.com/en-us/windows/uwp/porting/apps-on...
I'd still call it something we hope to see in the future, instead of a working proof of concept.
https://www.youtube.com/watch?v=OhESSZIXvCA
And you can actually download Windows on ARM from Microsoft Insider Preview for Free. And run it on top of Parallels Desktop 16.