Post with Transparent Background AND use Adobe Express for Vid Overlay

I'm trying and failing to import a video with transparent background to overlay on another video in Adobe Express.  I've tried using Media Encoder about 8x with various permutations of a .MOV file using Export with Alpha via Media encoder and then choosing Alpha Prores 4444 with Alpha (I've tried Prores 4444 regular too, and other settings).  Every time I drag my huge video file into Adobe express over another video it renders out with a black background.  Is there a bug in Express?  Do I have to use Premier Pro to utilize transparent background or is it not rendering properly.  I'm completely baffled here.  Thanks folks!