Need help with Excel formula or VBA to list same data found with a sum of a related field

From your example and description, a simple formula-based approach can work.

Formula-based (No VBA) – Using UNIQUE + SUMIF (Excel 365)

F2:F100 = Object Code

I2:I100 = Amounts (the "% of Org Code" applied to transaction)

The output summary table will be in columns K and L.

In K2:

=UNIQUE(F2:F100)

In L2:

=SUMIF(F2:F100, K2, I2:I100)

Then drag down.

Wrap it in SORT() if you want it alphabetically sorted:

=SORT(UNIQUE(F2:F100))

Of course you can use VBA too…your choice

VBA Script to Auto-Summarize Object Codes

This is a great option if:

You want a "clean button click", or you don't want formulas all over your sheet, or you want to paste in new data and auto-refresh the summary.

Sub SummarizeObjectCodes()
    Dim ws As Worksheet
    Dim lastRow As Long
    Dim dict As Object
    Dim objCode As String
    Dim amount As Double
    Dim i As Long
    Dim outRow As Long
    
    Set ws = ActiveSheet
    Set dict = CreateObject("Scripting.Dictionary")
    
    ' Identify last row with data
    lastRow = ws.Cells(ws.Rows.Count, "F").End(xlUp).Row
    
    ' Loop through object codes
    For i = 2 To lastRow ' assuming headers in row 1
        objCode = Trim(ws.Cells(i, "F").Value)
        If objCode <> "" Then
            amount = ws.Cells(i, "I").Value
            If dict.exists(objCode) Then
                dict(objCode) = dict(objCode) + amount
            Else
                dict.Add objCode, amount
            End If
        End If
    Next i
    
    ' Output summary starting from column K
    outRow = 2
    ws.Cells(1, "K").Value = "Object Code"
    ws.Cells(1, "L").Value = "% of Org Code (Total)"
    
    For Each objCode In dict.Keys
        ws.Cells(outRow, "K").Value = objCode
        ws.Cells(outRow, "L").Value = dict(objCode)
        outRow = outRow + 1
    Next objCode
    
    MsgBox "Object Code Summary Generated!", vbInformation
End Sub

'Code is untested back up your file first.

Don’t forget to Save the file as .xlsm

My answers are voluntary and without guarantee!

Hope this will help you.