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Happy to answer your questions
The pre-installed Ganglia UI is not modifiable in that way. If you want to create custom dashboards, you should set up your own monitoring system by using Azure Log Analytics.
One option is to use Azure Monitor + Power BI dashboards: https://learn.microsoft.com/en-us/azure/architecture/databricks-monitoring/
Monitoring and Logging in Azure Databricks With Azure Log Analytics and Grafana: https://cloudarchitected.com/2019/04/monitoring-azure-databricks/
Hope this helps.