Same issue here. I found that if i played around with the mac resolution outside of the game while it is running (using RDM) I could sometimes get it to behave, but haven't found repeatable steps to doing that yet. Like changing from 1680x1050 hiDPI to 1680x1050 not hiDPI and back flipping from desktop to full screen game a few times and eventually got it to show clearly. Might have more to do with the switching desktops than the resolution...who knows. This is on a 2018 MBP freshly updated to Catalina.
Anyone out there see the update on standalone? Looks like Steam and Chrome both have been updated, but my standalone (which is my preferred) still says new build imminent. Just me, or everyone? CaptTripz