How to pivot Multiple Columns

Assuming all of the ID's have all of the Milestone's listed in proper order, You can:

• Group by ID
• For each sub-table
  
  • Select the ID and Milestone columns and UNPIVOT other columns
  • Merge the Milestone and Attribute column => the new column headers
  • Remove the original columns and more the new merged column to Column2
  • Transpose the resultant table
    • Remove the top row and make the next row the new headers
• Re-Expand the grouped table

In the code below, change line 2 to reflect your actual data source

let
    Source = Excel.CurrentWorkbook(){[Name="Table7"]}[Content],
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"ID", Int64.Type}, {"Milestone", type text}, {"Actual Completion Date", type date}, {"Actual Start Date", type date}, {"Active", type text}, {"Activity Status", type text}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"ID"}, {
        {"Transpose", (t)=>
            let 
                #"Unpivoted Other Columns" = Table.UnpivotOtherColumns(t, {"ID", "Milestone"}, "Attribute", "Value"),
                #"Inserted Merged Column" = 
                    Table.AddColumn(
                        #"Unpivoted Other Columns", "Merged", each Text.Combine({[Milestone], [Attribute]}, " - "), type text),
                #"Removed Columns" = Table.RemoveColumns(#"Inserted Merged Column",{"Milestone", "Attribute"}),
                #"Reordered Columns" = Table.ReorderColumns(#"Removed Columns",{"ID", "Merged", "Value"}),
                #"Transposed Table" = Table.Transpose(#"Reordered Columns"),
                #"Removed Top Rows" = Table.Skip(#"Transposed Table",1),
                #"Promoted Headers" = Table.PromoteHeaders(#"Removed Top Rows", [PromoteAllScalars=true])
            in #"Promoted Headers"}}),

    #"Column Names" = Table.ColumnNames(#"Grouped Rows"[Transpose]{0}),
    #"Data Types" = List.Transform(#"Column Names", each if Text.EndsWith(_, "Date") then {_, type date} else {_, type text}), 
    #"Expanded Transpose" = Table.ExpandTableColumn(#"Grouped Rows", "Transpose", #"Column Names"),
    #"Set Data Types" = Table.TransformColumnTypes(#"Expanded Transpose", #"Data Types")
in
    #"Set Data Types"