VirtualBox 3D Acceleration

Are virtualbox guest additions fully functional? I.e. desktop resolution
and copy/paste from/to VM?

AnonymousUser via Whonix Forum:

Could the RAM-adjusted graphics code have something to do with this - if the mod is not contained in stock Debian?

RAM Adjusted Desktop Starter (rads) ? No. The only
difference is “start lightdm” vs “not start lightdm” (not start desktop
environment). Once desktop environment (lightdm) is started it is the
very same.

Another possible clue:

I now have an error update-initramfs: failed for /boot/initrd.img-4.19.0-6-amd64 with every apt upgrade now. Can’t find the link right now but a week ago I found vbox forums thread discussing an idea where the guest kernel needs to reconfigure each time you change from VBoxVGA to VMSVGA, etc? So it may be related?

Not sure if related (virtualbox guest additions installation does not
result in initramfs update) but this could be much more serious (prevent
boot). Please open a separate forum thread for this with full error message.