Hi @Christophe_Journel and @DennisLoos,
In 7.2, we allowed Filebeat to ship its monitoring data directly to a Monitoring Elasticsearch cluster (which might be separate from your Production Elasticsearch cluster, where you send the log data being harvested by Filebeat). The new monitoring.* settings introduced in 7.2 let you set the Monitoring cluster for Filebeat.
Now, if your output is elasticsearch, then we know which Elasticsearch cluster your Filebeat is sending its logs data to. In that case the Monitoring UI can correctly associate the Filebeat instance with that Elasticsearch cluster.
However, if the output is something other than elasticsearch, we cannot know if the logs data is ending up in an Elasticsearch cluster. So the Monitoring UI shows the Filebeat instance in a "Standalone Cluster".