When you have to see the Sum, Count, AVG of numeric columns in a subgrid, what is the easiest way? Export to Excel right? Now, there is an easier way: Aggregate Grid PCF Control. View Aggregates directly from Subgrid. This PCF control will list all numeric and currency columns in the view at the footer area, you just have to select the required column. This is not a production-ready control(I wanted to give life to an idea that came in during COVID19 lockdown) you can get the source code and unmanaged solution from here.
CSS & Grid design is from hovering list By Danish Naglekar.