You are trying to build a new DX Dashboard based on following out of the box DX Dashboard.
UIM: Top 10 Devices By Utilization
You would like to have data reported for one or more Groups and sub group(s) by selecting drop down list (variables).
On the UIM side there are groups that have sub groups. So, in this case there needs to have an option for first selecting one or more Groups, and then further selecting one or more sub groups (based on first selecting), and then showing the data for devices that only exists in selected Groups and sub groups.
Reconfigured the copy of the out of the box DX dashboard UIM: Top 10 Devices By Utilization.
Made Group first and adjusted Host variable with Expression uim.groups = $Group