Every now and then I have a problem after installing a new OS in virtualbox. All goes well until I head for fullscreen (RCTL+F)
It goes fullscreen, it works but the screen is greyed over, to @ half the brightness. Others have reported a black screen.
Go in to the Settings > User Interface section of your VM from the Virtualbox main screen
Untick Mini Toolbar and Save
Fullscreen should now work 🙂