Keynote - Export to Movie, transparent background checkbox not an option

I am trying to export a movie on keynote with a transparent background and the option just isn't even there. How do I change this? Is this an update issue? Or an OS issue? What is going on? See photo below. Only gives me options for resolution. No mention of ProRes 4444 or anything. Help! (And yes, on the slide, I had selected no fill for the background).