WetGeek I'd like to get to the bottom of this, just for my own peace of mind.
I created a new Budgie VM, and saved a "Fresh Installation" snapshot before changing anything. Then I remembered that at one time we needed to change the video setting. Rather than use the default, this time I changed that to VBoxSVGA, and created another snapshot.
After that, I ran an update that included 348 upgraded packages, and this time a reboot resulted in a running machine. I don't remember changing that setting for the previous Budgie VM, but perhaps I did. I'd been using it and updating it for a pretty long time.
Anyway, if you have a Budgie VM that croaked after this week's update, be sure that your video support is set to VBoxSVGA. With that, my VM is running just fine.