Power query: Group by Date Column and keep Max for all other columns - Dynamic approach

You can create a dynamic List of functions, based on the column names, for both setting the data types, and also performing the aggregations in the Grouping.

In the aggregation transformation, C represents the column name; the underscore ( _ ) represents the subtable returned in the Table.Group function

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("TY7RDQAhCEN34dtExTv1ZjHuv4ZQMMdHTekjxbWoZs5cKRH0yPOa2UmhDqxBuyvDSZcBIV9TAtEi1A7RFwDa1UzIgC51v9Tg/9wK/BcRTIcFrXsf", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Date = _t, Column1 = _t, Column2 = _t, Column3 = _t, Column4 = _t]),
    
//List of column names EXCEPT for "Date"
    maxCols= List.RemoveItems(Table.ColumnNames(Source),{"Date"}),

//set data types
    #"Changed Type" = Table.TransformColumnTypes(Source,
        {{"Date", type date}} & List.Transform(maxCols, each {_, Int64.Type})),

//Group and create list of aggregation functions
    group = Table.Group(#"Changed Type",
            "Date",
            List.Transform(maxCols, (C) => {C, each List.Max(Table.Column(_, C)), type number})
)

in
    group

Source Data

Typed

Results