I just figured out how to test Windows 11 in a VM on macOS:
- Grab the latest Windows 10 Insider Preview (21354) and install it in Parallels 16 or later
- Sign up for Windows Insider builds here: Windows Insider (requires a microsoft account but is otherwise free)
- Install the Windows 10VM
- Inside Windows 10, go to Settings / Update / Windows Insider Program and turn on the Dev channel.
- Press the Check Updates buttons a few times
- Windows 11 will (eventually) install.