I know that the supported Gradle version is 5.3, but I decided to try with the version of Gradle I had installed (5.6.2) and things appeared to be working. Until I got a message about QuantumMessagesBundle not found when I tried to run my test app. Eventually I narrowed it down to the build with Gradle 5.6.2 not having the .properties files in the javafx.graphics.jar.
I would normally shut up and use ./gradlew like I'm supposed to, but with the recent release of Java 13, and the fact that Gradle 5.3 (and 5.6.2) can't handle the class file version from Java 13, I figured a Gradle upgrade is going to be necessary soon. Cheers, Scott