Showing Count of Features by Attribute in Arcade Popup

I have a survey that I’m running through Survey123. I want to display the results in a web map that clusters points. In the popup for each cluster, I would like it to display how many features from each submitter are within the cluster. How do I enter that into an Arcade expression to get the popup to display correctly?

The field is installed_by, which has a string for the name of the installer, and the output should look like:

Total – 23
Al – 5
Bill – 10
Cindy – 8