The NodeJS site makes available tar.gz package for all (except windows) platforms. The drop down is not populated depending on the file extension. The reason why you do not see version > 6.6.0 is because your jenkins instance does not download the hudson.plugins.nodejs.tools.NodeJSInstaller.json with updated list of available version.

Thank you for the reply, but i wonder why the "hudson.plugins.nodejs.tools.NodeJSInstaller.json" is not beeing downloaded although I can and do install all plugins from the web, so there's no proxy configuration or firewall that prevents any downloads.

Is there a way to find the cause why the json is not beeing updated?

I triggered a manual update of the Update metadata and found this in the Jenkins Log

Jan 23, 2018 1:14:15 PM WARNING hudson.model.DownloadService$Downloadable updateNow
No tool installer metadata found for hudson.plugins.nodejs.tools.NodeJSInstaller

Update:
trying the following did work, but still no updated metadata:

for (d in DownloadService.Downloadable.all()) {
  println("${d.url} -> ${d.updateNow().kind}");
}

http://updates.jenkins-ci.org/updates/hudson.plugins.nodejs.tools.NodeJSInstaller.json -> OK

Update 2:
I created a Logger for the Download-Service and it says:

Could not load json from http://updates.jenkins-ci.org/stable/updates/hudson.plugins.nodejs.tools.NodeJSInstaller.json
java.io.FileNotFoundException: http://mirrors.jenkins-ci.org/updates/stable-2.89/updates/hudson.plugins.nodejs.tools.NodeJSInstaller.json.html?id=hudson.plugins.nodejs.tools.NodeJSInstaller&version=2.73.3

well that's diappointing but seems to be a broader problem and not related to the NodeJS plugin.

Thank you for your help to figure this out.

I found the issue. In our slightly older installation (2.73.3) the update site was configured to:

http://updates.jenkins-ci.org/stable/update-center.json

but with the update to 2.89.1 LTS the following change was introduced:

Default the built-in Jenkins Update Center URL to https://updates.jenkins.io instead of obsolete HTTP endpoint. This requires a JRE compatible with Let's Encrypt, e.g. Oracle JRE 8u101. (pull 2996)

This seems to have broken our older installation, so I changed the update site to:

https://updates.jenkins.io/stable/update-center.json

and so the metadata updates are working again.

Strange enough a local Jenkins with version 2.73.3 has the plugin/metadata update URL

http://updates.jenkins-ci.org/update-center.json

and this is working as intended too.

All json files are here https://updates.jenkins.io/updates/

in case download it and copy to the ${JENKINS_HOME}/updates/ folder and restart