Thank you from me, as well, as I just upgraded to Catalina and ran into this same issue. I was in "Windowed (Fullscreen)" mode, but switching to plain "Windowed" fixed it, and then I was able to switch back to "Windowed (Fullscreen)" again.
Edit: I exited and restarted the game as a test, and I get the white screen all over again when it starts in "Windowed (Fullscreen)," which is a pain; but at least now I know how to deal with it.