From OpenSCADAWiki
Where VBoxVGA and VBoxSVGA are the original VirtualBox Graphics Controllers who need the own guest driver for true work and that driver is missing in the main repositories the modern Debian for the LiveDisks build. So, the LiveDisks start mostly with the "fbdev" video driver, which however worked fine till VirtualBox 6.1 and you could change the display resolution from default 800x600 one in the loaded system, reload and got need resolution. Now these Graphics Controllers are not recommended by VirtualBox and cause often to lose the keyboard and mouse keys in the all host system.