As reported by https://kotlinlang.slack.com/archives/C4W52CFEZ/p1730232596622489
users still have to write:

dependencies {
    add("kspJvm", "org.jetbrains.kotlinx.dataframe:symbol-processor-all:${libs.versions.dataframe.get()}")
}

in their build files manually to get the extension properties to be generated. We need to check whether this can be done automatically.