I had this problem as well running a newly installed version of VirtualBox (VirtualBox 6.0). I tried installing the aforementioned packages but had no luck. My solution was simpler than I had anticipated. While the machine is powered off, go to:
Settings (of the VM) > Display > Graphics Controller > and select "VBoxVGA"
VirtualBox had set this option to "VMSVGA" by default for me. Fortunately, I noticed this subtle difference when comparing the settings between some of my virtual machines. I hope this works for you as well!