Lists 365 JSON - group header based on condition

Question

Similar to the example here: Example: Color coded group header with aggregate

I am trying the group header text in the list view to show the number of tasks that are NOT 'Completed' in the 'Status' choice column.

Here's my JSON, can someone help me out with this?

{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/v2/row-formatting.schema.json",
  "groupProps": {
    "hideFooter": true,
    "headerFormatter": {
      "elmType": "div",
      "style": {
        "flex-wrap": "wrap",
        "display": "flex",
        "box-sizing": "border-box",
        "padding": "4px 8px 5px 8px",
        "border-radius": "6px",
        "align-items": "center",
        "white-space": "nowrap",
        "overflow": "hidden",
        "margin": "1px 4px 4px 1px"
      },
      "attributes": {
        "class": "ms-bgColor-neutralQuaternary"
      },
      "children": [
        {
          "elmType": "div",
          "children": [
            {
              "elmType": "span",
              "style": {
                "padding": "5px 5px 5px 5px",
                "font-weight": "500"
              },
              "txtContent": "@group.fieldData.displayValue"
            }
          ]
        },
        {
          "elmType": "div",
          "forEach": "iterator in @currentField",
          "children": [
            {
              "elmType": "div",
              "style": {
                "display": "=if([$iterator.columnDisplayName] == 'Status' && [$iterator.value] != 'Completed', 'flex', 'none')",
                "flex-direction": "row",
                "justify-content": "center"
              },
              "children": [
                {
                  "elmType": "div",
                  "txtContent": "=' pending tasks: ' + Number(@group.count - Number([$iterator.value]))",
                  "style": {
                    "font-weight": "500"
                  }
                }
              ]
            }
          ]
        }
      ]
    }
  }
}

Answer 1

The @group object provides access to the grouped column's data, display name and item count.

If you want to show the number of tasks that are not 'Completed' in the 'Status' choice column, it's necessary to group by the choice column.

If you group by another column instead of the choice column, it's not possible to get the count via @group.

--------------------Update-----------------

Per my test, It seems that the error prevent aggregate from working, we suggest you open a service request to Microsoft.