I need Help With A Date Formula

I need this file...
C:\Users\Mohammed\Downloads\Test Date.xlsx, but what I see from your query is that you didn't read carefully my Note!

Try this, but this time do not add it as custom column. Open Advanced Editor, delete whole query and paste there this one.

let
    Source = Excel.Workbook(File.Contents("C:\Users\Mohammed\Downloads\Test Date.xlsx"), null, true),
    Table1_Table = Source{[Item="Table1",Kind="Table"]}[Data],
    TrimmedColumnNames = Table.TransformColumnNames(Table1_Table, Text.Trim),
    ChangedType = Table.TransformColumnTypes(TrimmedColumnNames,{
    {"Est Close Date", type date}, {"Close Date", type date}}),
    Ad_EstCloseYear = Table.AddColumn(ChangedType, "Est Close Year", each Date.Year([Est Close Date]), Int64.Type),
    Ad_CloseYear = Table.AddColumn(Ad_EstCloseYear, "Close Year", each Date.Year([Close Date]), Int64.Type),
    Ad_NewCloseDate = Table.AddColumn(Ad_CloseYear, "New Close Date", each 
        [ today = Date.From(DateTime.FixedLocalNow()),
          thisYear = Date.Year(today),
          result = if [Deal Stage] <> "Won" then null else
                   if [Close Date] = null and [Est Close Year] = thisYear then today else
                   if [Close Date] = null and [Est Close Year] < thisYear then [Est Close Date] else
                   if [Close Year] > [Est Close Year] then [Est Close Date]
                   else [Close Date]
        ][result], type date)
in
    Ad_NewCloseDate