You could EVALUATE your current formula and output the array:
Sub test()
Dim var As Variant
Dim wsSum As Worksheet, wsDet As Worksheet
Dim lrSum As Long, lrDet As Long
Dim SumAB As String, DetF As String, DetA As String, DetB As String
Set wsSum = Sheets("Summary")
Set wsDet = Sheets("Detailed")
lrSum = wsSum.Range("A" & Rows.Count).End(xlUp).Row
lrDet = wsDet.Range("A" & Rows.Count).End(xlUp).Row
SumAB = wsSum.Range("A2:B" & lrSum).Address(, , , 1)
DetF = wsDet.Range("F2:F" & lrDet).Address(, , , 1)
DetA = wsDet.Range("A2:A" & lrDet).Address(, , , 1)
DetB = wsDet.Range("B2:B" & lrDet).Address(, , , 1)
var = Evaluate("BYROW(" & SumAB & ",LAMBDA(x,TEXTJOIN("" | "",TRUE,UNIQUE(FILTER(" & DetF & ",(" & DetA & "=INDEX(x,,1))*(" & DetB & "=INDEX(x,,2)))))))")
wsSum.Range("F2:F" & lrSum) = var
End Sub