So i believe you can do either group summaries or detailed info for individual computers, but not both in the same report. It sounds like you might be looking for something like this:
I named this report: "Computer Update Status for selected WSUS Target Groups".
All of these fields are from the Computer Update Status with Approval Information Datasource:
In the top part (report definition):
Name (Update Server)
Update Installation State (Friendly Name)
Update Approval Action (Friendly Name)
Domain or Workgroup (Update Server)
In the bottom part (filter criteria):
Group Memberships contains Prompt: Please enter the WSUS Target Group Name
Note: when you run it and type the (part of) the group name you wish to report on, you have to click OK twice for the report to run. Not sure why, but it's a thing.
When i run it, here is the prompt for "group name contains":
and here is what the report results will show; this could now be exported to Excel, or you could group by Computer Nmae or Update Title in the results pane by dragging those column header(s) up to the dark grey area right above the column headers: