VirtualBox traps CTRL-ALT when focused, interferes with workspace switching

Solution 1:

At present there is no option to customize the capture behavior of host keystrokes in VirtualBox. It is either always "Auto Capture Keyboard" or never so. This can be defined in the application preferences from Virtual Box Manager preferences dialog.

A convenient way to temporarily toggle host keyboard capturing is pressing the Host-key once. By default this is set to RightCtrl but on my system I set it to RightShift as shown below:

If auto-capture was enabled we can use the host keys until we toggle back.

In case we had used AltTab application switcher the guest restores the default keyboard capture state when the guest windows gets focus again.