Exactly how to do this will depend on how you are actually using all of the tables in this app. I’ll make some assumptions for now
In the Sample app there is a Products table. In that table there is a value named “Current Inventory” which I assume is to be the count of that particular product. Let’s say its a certain style and size of a Hoodie. BUT, you will have different sizes and styles of Hoodies, each with their own Product row representing them.
All of these have the category of “Hoodies” in the Product Category table
So…if you wanted to also show the number of ALL Hoodies, you would need to ADD a Virtual Column called, for example, “Total Items” in the Product Category table.
Then you would set the “App Formula” of this column to an expression similar to:
SUM(SELECT(Products[Current Inventory], [Product Category] = [_THISROW].[Category]))
First, the SELECT() returns a List of [Current Inventory] where Product Category matches Category. In this case “Hoodies”
Second, SUM(), obviously, will add all of the values in the list together to give you a total.
This expression will be applied to each Category table row separately so you get a total count for each.