An updated Mac app with support for Catalina is now live! Details here.

Thanks for pointing this out. We'll get this fixed. In the interim, here is a workaround to get it installed: In macOS Catalina and macOS Mojave, when an app fails to install because it hasn’t been notarized or is from an unidentified developer, it will appear in System Preferences > Security & Privacy, under the General tab. Click Open Anyway to confirm your intent to open or install the app.