Merge and update History table from Update table having new or updated values

Read this for info on Formula.Firewall:

https://www.thepoweruser.com/2019/03/12/data-privacy-and-the-formula-firewall/

(The simplest solution is the 'Always ignore Privacy Level settings' under Query Options > Privacy.)

You can use whatever column or combination of columns you'd like to define what you consider unique. You can certainly drop the Product column. and only group over ProductKey.

Here's a bit more dynamic version of the query where I've added steps to generate lists of column names.

let
    Source = Excel.CurrentWorkbook(){[Name="UpdateableTable"]}[Content],
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"ProductKey", Int64.Type}, {"Product", type text}, {"Status", type text}, {"Date", type date}, {"Forecast", Int64.Type}, {"Out of stock", type text}, {"Manual1", type text}, {"Manual2", type text}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Version", each 0, Int64.Type),
    #"Appended Query" = Table.Combine({#"Added Custom", NewData}),
    #"Grouped Rows" = Table.Group(#"Appended Query", {"ProductKey"}, {{"All Rows", each Table.Max(_, "Version"), type record}}),
    ColumnNames = List.Select(Table.ColumnNames(NewData), each _ <> "ProductKey"),
    #"Expanded All Rows" = Table.ExpandRecordColumn(#"Grouped Rows", "All Rows", ColumnNames, ColumnNames),
    #"Merged Queries" = Table.NestedJoin(#"Expanded All Rows", {"ProductKey"}, #"Changed Type", {"ProductKey"}, "Expanded All Rows", JoinKind.LeftOuter),
    ManualColumns = List.Difference(Table.ColumnNames(#"Changed Type"), Table.ColumnNames(NewData)),
    #"Expanded Expanded All Rows" = Table.ExpandTableColumn(#"Merged Queries", "Expanded All Rows", ManualColumns, ManualColumns)
in
    #"Expanded Expanded All Rows"