in the current Beta of 10.15MacOS you can not open file or import anything over the menu, because no finder window opens.
I doubt there will be any changes to address macOS 10.15 issues until it’s released. It’s a moving target. For example, I can’t even run Voxelizer nor any other unsigned app in the latest macOS beta: I get a security error. Fortunately, my Mac mini that I use for a home server is still running Mojave.
Your problem is a security feature, you can allow the app to start in the settings ->Security.
After this message there will appear a allow button with a message to the app.
Now, Catalina is released, when will be an update?