Create Table based on another table according to criteria

This is easier to do in query.  Below is some example M on how to do it with your data.  To see how it works, just create a blank query, go to Advanced Editor, and replace the text there with the M code below.  The modified #"Grouped Rows" step is the one you will need to adapt to your query.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("bY1BDsAgCAS/YjybIAvaxxj//402GEqNvW3YYXaMzLlkJiZU1CeCmkehvuIsCwPBuxZYsh6r1wDkdfavSGwP9Vhxk5iJNQA+Zx3sJPHtBjXy+i/Sdmn7Zd4=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Item = _t, Date1 = _t, Date2 = _t, Date3 = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Item", Int64.Type}, {"Date1", type date}, {"Date2", type date}, {"Date3", type date}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Item"}, {{"Date1", each if List.Contains([Date1], null) then null else List.Max([Date1]), type nullable date}, {"Date2", each if List.Contains([Date2], null) then null else List.Max([Date2]), type nullable date}, {"Date3", each if List.Contains([Date3], null) then null else List.Max([Date3]), type nullable date}})
in
    #"Grouped Rows"

If this works for you, please mark it as the solution.  Kudos are appreciated too.  Please let me know if not.

Regards,

Pat