Wow, VirtualBox does have a GUI option to detach so that you can operate in “headless” mode without the virtual machine GUI window present on your desktop, but it came about with a hide-and-seek game of GUI reorganization.
20190718/DuckDuckGo virtualbox hide window daemon vm
20190718/https://www.virtualbox.org/ticket/2597
20190718/DuckDuckGo virtualbox start vm daemon no gui
Beware! You MUST start a VM as headless via the command line or else you will not get the “detach GUI” option in the GUI.
VBoxManage startvm --type headless <name>