I have a freshly installed Windows 10 from the latest MS ISO, Windows 20H2. It was installed on my internal drive that had been freshly zeroed out and then Catalina installed on it, followed immediately by running Bootcamp assistant. I have not even installed Bootcamp within the Windows 10. --- all of which is to say, there is absolutely no possible left-over cruft on the drive interfering. The system works when I boot directly into the partition. When I am booted to Catalina, and I tell Parallels 16 or Parallels 15 to attach to the partition, when the system starts, I get a message that the PC needs to be repaired, 0x0000000f and that a device is missing. I suspect that the situation is related to using a newish Windows release, possibly even the same root cause as https://forum.parallels.com/threads...-to-be-repaired-error-code-0xc000000f.347815/ In the meantime, a VM of Windows 20H2 that I installed directly (not through bootcamp) is working fine.
Update: I was able to "Import from Bootcamp". The configuration step took quite a while after I had already been told the VM was ready, but it did finish eventually, and I can start the machine without difficulty. As this was exactly the same source partition as the one that fails complaining about missing device, then the implication is that the problem does not arise directly from the content of the partition (though it is possible that there is an interaction with the Windows version.)
I spoke too soon. After I let Windows install the "high priority" system updates, rebooting the imported bootcamp now gives the same "need to repair / device cannot be found" error. I deleted the imported bootcamp pvm (including empty trash), but now it does not give me the option to import from bootcamp. IMHO, import from bootcamp should always be permitted as long as bootcamp is detected.
