transforming excel sheet in power query editor

I am assuming that you must have multiple rows with the same notification but different Stat and Date, and that your example is not realistic.

Perhaps a more realistic data source would look like:

That being the case, the below might be what you want:

let
    Source = Excel.CurrentWorkbook(){[Name="Table2"]}[Content],
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Notification", Int64.Type}, {"Stat.", type text}, {"Date", type date}}),
    
//will be used below in Pivot
    Stats = List.Sort(List.Distinct(#"Changed Type"[#"Stat."])),

    fieldTypes = List.Repeat({type nullable date}, List.Count(Stats)),
    rowColumnTypes = List.Transform(fieldTypes, (t) => [Type = t, Optional = false]),
    rowType = Type.ForRecord(Record.FromList(rowColumnTypes, Stats),false),

    #"Grouped Rows" = Table.Group(#"Changed Type", {"Notification"}, {
        {"Pivot", each Table.Pivot(_, Stats,"Stat.","Date"), type table rowType}}),
    #"Expanded Pivot" = Table.ExpandTableColumn(#"Grouped Rows", "Pivot", Stats)
in
    #"Expanded Pivot"

producing: