VirtualBox has default host key – Right Ctrl. You use this key to operate your VM, eg. Right Ctrl + F – toggles full screen.
One friend of mine, Sergey Arhipenko, gave me a recommendation which I’d like to share with you. Change this key to something less important, e.g. Application key
This will allow you to keep using Right Ctrl as usual. And I found this is very handy.
To change it open Oracle VM VirtualBox Manager > File > Preferences > Input > Virtual Machine > Host Key Combination