Determine invoice category based on highest-value line item

kirvis  with PQ

List.Max(
      Table.SelectRows(
        CT,
        (r) =>
          r[Invoice number]
            = [Invoice number] and r[Value]
            = List.Max(Table.SelectRows(CT, (q) => q[Invoice number] = [Invoice number])[Value])
      )[Category]
    )

let
  Source = Table.FromRows(
    Json.Document(
      Binary.Decompress(
        Binary.FromText(
          "i45WMlTSAWOn/KKU1MTSChDX0EApVgciZQTEPol56aWpKfnJIDlTuJQxEDvmFCcmpwIZphBxIyymmRrApYyQtRgbACViAQ==",
          BinaryEncoding.Base64
        ),
        Compression.Deflate
      )
    ),
    let
      _t = ((type nullable text) meta [Serialized.Text = true])
    in
      type table [#"Invoice number" = _t, #"Line item" = _t, Category = _t, Value = _t]
  ),
  CT = Table.TransformColumnTypes(
    Source,
    {
      {"Invoice number", Int64.Type},
      {"Line item", Int64.Type},
      {"Category", type text},
      {"Value", Int64.Type}
    }
  ),
  #"Added Custom" = Table.AddColumn(CT, "maxCAT", each List.Max(
      Table.SelectRows(
        CT,
        (r) =>
          r[Invoice number]
            = [Invoice number] and r[Value]
            = List.Max(Table.SelectRows(CT, (q) => q[Invoice number] = [Invoice number])[Value])
      )[Category]
    ))
in
  #"Added Custom"

with DAX

_maxCAT =
VAR _partition =
    ALLEXCEPT ( 'Table', 'Table'[Invoice number] )
VAR _val =
    CALCULATE ( MAX ( 'Table'[Value] ), _partition )
RETURN
    CALCULATE ( MAX ( 'Table'[Category] ), 'Table'[Value] = _val, _partition )