After looking into the responsible msi-bundler, I found this fragment:
List<String> commandLine = new ArrayList<>();
// (...)
commandLine.add("-ext");
commandLine.add("WixUtilExtension");
if (enableLicenseUI || enableInstalldirUI) {
commandLine.add("-ext");
commandLine.add("WixUIExtension.dll");
}
// (...)
This means WixUtilExtension is always added, and when having the user to choose the installation target directory, the extension WixUIExtension gets added too.
To have the user choose the target installation directory, you have to set this inside the jfx-configuration-part:
jfx {
// ...
bundleArguments = [
'installdirChooser': true
]
// ...
}
https://github.com/FibreFoX/javafx-gradle-plugin/issues/101
Disclaimer: I'm the creator of the javafx-gradle-plugin