问题是插件org.javafxports.jfxmobile与Gradle 6不兼容.降级Gradle版本5.

The issue is that the plugin org.javafxports.jfxmobile is not compatible with Gradle 6. Downgrade Gradle version 5.

由于Gradle 5不支持Java 13，因此您还应该将Java降级为Java 11.

Since Gradle 5 do not support Java 13 you should also downgrade Java to Java 11.