Oh I'm quite aware that the sample code isn't intended to be a "real" application; I only used it to test the approach, and to see if it was any better than Parallels at the same task (it is, because I was able to directly create the VM from the the beta image). In fact, it was very exciting to have so much functionality in sample code. What's lacking is Parallels' VM. It doesn't share the clipboard, and doesn't allow dragging and dropping of files between the host and guest Finders, something that does work for the other guest OSes like Windows.
What is lacking in the macOS virtualization framework is documentation. It's not clear, for example, how one would change the display configuration of a running VM (e.g. in response to a VM window size change), or how to set up the shared clipboard, or what a "memory balloon" device is.
I've already filed a bug about not being able to log into iCloud, which has also been reported on this forum by many others. FB12006346
Looking at the Console, it definitely seems to be a self-signing issue.
So I go to sign my app, but I can't. I don't know why, but I get errors saying it couldn't communicate with Apple, which seems unlikely, and that no provisioning profile for my app was found. But it's supposed to be managing that automatically.
THIS IS TOO HARD.