Allowing Host notification pop ups in guest Virtualbox session that is full screen
As someone who has to use VB at work a lot one solution I found was to make the virtual box window huge and hiding the task bar beneath my real one. this does come with the one negative of having to hide your task bar but anything you need from it can still be accessed from the windows key. however since VirtualBox isn't technically fullscreen it doesn't block your notifications. or just have outlook for your phone but I know that isn't always the best solution.
Edit, I didn't realize ubuntu was the OS you were running on in VB, that being said there are hotkeys that work just as well and if memory serves me well alt f1 does the same thing as the windows key but for ubuntu.