I just went through this issue, and the only way I managed to get elasticsearch to run was to edit the elasticsearch.yml file and add xpack.ml.enabled: false to the bottom of the file. Apparently it disables the machine learning.
Elasticsearch is running, but now I have a Magento issue. Not sure if it will still work with Magento this way, but at least now it starts.
That doesn’t seem to work out of the box, unless an elastic user is configured manually. The easiest work-around would be to edit /etc/elasticsearch/elasticsearch.yml and set xpack.security.enabled to false and restart elasticsearch.service.