When you secure your Elasticsearch with User Authentication you need to add credentials to the Graylog configuration to be able to use the secured Elasticsearch cluster with Graylog.
Now that x-pack has been deprecated, what are my options? do i need to subscribe to ‘Elastic Stack’ ?
I can understand your frustration.
X-Pack requires the default distribution and can not be installed as a plugin on the OSS version.
I believe this is more on the Elasticsearch side then it is from Graylog.