Is there a guide to integrate Grafana with Zammad through Elasticsearch?

I’ve seen many posts in many websites displaying only a part of the whole story and I can’t get the pieces in the right place… is there a tutorial that explains how to get from A to B regarding Zammad and Grafana dashboards?

Yes and no.

This page lists limitations and expactations (from our end):
https://docs.zammad.org/en/latest/appendix/reporting-tools-thirdparty.html

and this page actually tells you on how to create / import datasources and dashboards:
https://docs.zammad.org/en/latest/appendix/reporting-tools-thirdparty/grafana.html

Both pages do not contain on how to adjust Elasticsearch’s security settings (if required) nor how to install Grafana. That’s out of Zammad’s scope - the vendors to have excellent documentation on this regard.