Question about EventSystem and handling in game world

So here it is, I have a game menu in my world (screen space overlay) and I'm a bit not sure how to know that input was not handled on the ui side and I'm safe it to use it in my world. One thing that came to my mind is that I should have a background panel with events, which catches input and send to my world handlers. Or maybe there is some sort of alternative? Maybe even EventSystem.RaycastAll, check if no gui was hit and go from there? Any suggestions from your experience are welcome.

Edit: Is EventSystem bound to only UI or is it possible to use it in game world?