Most Recent Transaction

Here is one way.

It assumes that, unlike your example, there will be more than a single combination of Operation/Part Number.

• Group by Part Number/Operation
• Select StdTime corresponding to the Max Labour Operation

let

//Change Source line to reflect your actual data source
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlTSUQpPzUkBUoZGxhGRUUCGkbFSrE60khFuKWPcUia4pUyxSZmCpcxwS5njlrLAJmUOlrLELWVogEMuFgA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Labour Booking" = _t, Operation = _t, #"Part Number" = _t, StdTime = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{
        {"Labour Booking", Int64.Type}, {"Operation", type text}, {"Part Number", type text}, {"StdTime", Int64.Type}}),
    
    #"Add Current StdTime" = Table.Group(#"Changed Type", {"Operation", "Part Number"}, {
        {"Current StdTime", (t)=> Table.AddColumn(t, "Current StdTime", each 
            [a=Table.SelectRows(t, each [Labour Booking] = List.Max(t[Labour Booking])),
             b=a[StdTime]{0}][b]),
            type table[Labour Booking=text,Operation=text, Part Number=text, StdTime=Int64.Type, Current StdTime=Int64.Type]
            }}),

    #"Removed Columns" = Table.RemoveColumns(#"Add Current StdTime",{"Operation", "Part Number"}),
    #"Expanded Current StdTime" = Table.ExpandTableColumn(#"Removed Columns", "Current StdTime", 
        {"Labour Booking", "Operation", "Part Number", "StdTime", "Current StdTime"})
in
    #"Expanded Current StdTime"