i tried to install the latest beta of Daslight 4 on Mac OS Catalina as you described here
But I don’t get the "open" button at the dialog to start the the install. There only the buttons "Show in Finder" and "OK".
The security settings for apps are set to "App Store and Developer", so this can't be the reason in my opinion.
It would be nice if someone could tell me who to install the latest beta on Mac OS Catalina.