How to select a product for the highest value

See the working here - Open a blank query - Home - Advanced Editor - Remove everything from there and paste the below code to test (later on when you use the query on your dataset, you will have to change the source appropriately. If you have columns other than these, then delete Changed type step and do a Changed type for complete table from UI again)

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WCgwMNDRS0lEyNDIGkhEREUqxOghRE5Cgi4sLWBBIuwaBBIxMTIGko6MjmrCxCZAMD0cVNQaZExSkFBsLAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [CODE = _t, VALOR = _t, PRODUCT = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"CODE", type text}, {"VALOR", Int64.Type}, {"PRODUCT", type text}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"CODE"}, {{"VALOR", each List.Max([VALOR]), type nullable number}}),
    #"Merged Queries" = Table.NestedJoin(#"Grouped Rows", {"CODE", "VALOR"}, #"Changed Type", {"CODE", "VALOR"}, "Grouped Rows", JoinKind.LeftOuter),
    #"Expanded Grouped Rows" = Table.ExpandTableColumn(#"Merged Queries", "Grouped Rows", {"PRODUCT"}, {"PRODUCT"})
in
    #"Expanded Grouped Rows"

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