Additional info: The OPEN file statements are shown below in bold. Is there an option to ignore the 'File Contains Macros' message?

Here is the macro code to open the files….
 Sub Process_one_File(folderPathname As String, registrationFileName As String)

  Dim sheetName As String
  Dim ok As Integer
  Dim lastRow1 As Long
  Dim lastRow2 As Long
  Dim sourceDataRange As Range
  Dim MasterDataRange As Range
  Dim itemRange As Range
  Dim itemCell As Range
  Dim clubAbbrev As String
  Dim r As Long
  
 
  ok = 1
  If registrationFileName = ThisWorkbook.Name Then ok = 0   ' skip this file
  If Left$(registrationFileName, 11) = "GSL-Entries" Then ok = 0   'skip backup copies of this file
  If ok = 0 Then Exit Sub

  'MsgBox registrationFileName
  
  ' ...  Begin by opeing the selected file, etc   (MAC version)
  If Application.OperatingSystem Like "*Mac*" Then
    Workbooks.Open filename:=folderPathname & ":" & registrationFileName, ReadOnly:=True
  Else
    Workbooks.Open filename:=folderPathname & "\" & registrationFileName, ReadOnly:=True
  End If

  '  ……  process the file…