If you need to target JDK 9+

[RaphaelFourdrilis]

JFoenix does support JDK 9+ now.

I managed to make it work this way:

build.gradle.kts:

dependencies {
    implementation("no.tornado:tornadofx:1.7.20")
    implementation("com.jfoenix:jfoenix:9.0.8")
    implementation("com.github.bkenn:kfoenix:0.1.3") {
        exclude("com.jfoenix:jfoenix")
    }
}

Thought I'd put it there if someone needs it, cheers!