Copy and Paste VBA many sheets

Try this.

Sub InsertColumns2()

Dim ws As Worksheet

   Application.ScreeUpdating = False
 
   For Each ws In ThisWorkbook.Worksheets
 
      With ws
 
          .Range("AM:AM").Copy
          .Range("AN:AN").PasteSpecial xlPasteValues
 
      End With 

    Next ws

    Application.ScreenUpdating = True

 End Sub