If I buy an OEM license for Windows 10 (home or professional?) will I be able to activate the Windows Insider programme to access the Windows ARM builds?
Strictly speaking purchasing a version of Windows 10 Home or Windows 10 Professional will not give you access to a license to Windows 10 on ARM. It is not possible to purchase a Windows 10 ARM license separately. Windows 10 for ARM is only sold with ARM devices with eligible processors.
While it might appear that Windows on ARM activates with a Windows 10 Home or Windows 10 Professional license users have reported that’s only temporary.
My activation issue is a little odder. I come up activated but a couple of hours later I get a message that my Windows is unactivated. A reboot resets it.
At this time you can only get an actual Windows 10 On ARM license is if you own a device with a Microsoft SQ1, Microsoft SQ2, Qualcomm Snapdragon 8cx, or Qualcomm Snapdragon 850 processor.
The fact an Insider Preview build actually can run on an M1 Apple device, within a Parallels VM, is likely unintentionally at this time.
Please see the linked Reddit page for how that poster did it. If you are part of the Windows Insider beta testing program, you do have access to Arm builds, but you (possibly?) need an active running version of windows to access them, I think?
You need a Windows installation to join the Insider Preview program but you don’t need one to download the virtual machine itself.
Windows 10 on ARM Insider Preview