I tried a lot, but just changing the graphics settings/graphics controller in the host machine's options from VMSVGA to VBOXSVGA started the Ubuntu VirtualBox immediately in the right resolution for me, i.e. 1920x1080.
I tried a lot, but just changing the graphics settings/graphics controller in the host machine's options from VMSVGA to VBOXSVGA started the Ubuntu VirtualBox immediately in the right resolution for me, i.e. 1920x1080.