The unix exec is marked as a document and not as an executable file. To fix this, right click on the application and click "Show Package Contents." Then navigate to Contents > MacOS > Vibrant Venture. Open the Terminal app and type "chmod u+x " and then drag the Vibrant Venture file. Press Enter, then go back, right click on the application again and click open, and when the security window pops up click open again, and now it works. The developer should fix this at some point.
Thanks so much!! This worked perfectly, not only for this game in particular but also some other games I've had trouble opening on my Mac. I'm not sure why this issue keeps popping up ever since I upgraded to Catalina but you're a lifesaver!