It should be possible operate a vehicle while simultaneously interact with some special user interface. This is probably a feature that could be implemented in the future of Fortnite creative where there are more UI capabilities in general.
The idea here is for example to drive a car while allowing the user to initiate some kind of a pop-up or overlay UI and interact with it through the d-pad (on controller) and temporarily disabling things like boost to reuse the A, B, X and Y key (on controller) to confirm or cancel ui actions.