Option Explicit

Private lCalc               As Long
Private lStatusbar          As Long
Private lEvent              As Long
Private lScreen             As Long
Private xFileSystemObject   As Object




Sub MainList()
     
    Dim folder              As Variant
    Dim xDir                As Variant
     
    ThisWorkbook.Worksheets(1).Cells.ClearContents
    Set folder = Application.FileDialog(msoFileDialogFolderPicker)
     
    If folder.Show <> -1 Then Exit Sub
        Call TurnOffFunctionality
            
            xDir = folder.SelectedItems(1)
                Set xFileSystemObject = CreateObject("Scripting.FileSystemObject")
                    Call ListFilesInFolder(xDir)
                        ActiveSheet.UsedRange.EntireColumn.AutoFit
    
        Call TurnOnFunctionality
 
 
 
    Set xFileSystemObject = Nothing
End Sub
 
Sub ListFilesInFolder(ByVal xFolderName As String)
     

    Dim xFolder             As Object
    Dim xSubFolder          As Object
    
    Set xFolder = xFileSystemObject.GetFolder(xFolderName)
     
    For Each xSubFolder In xFolder.SubFolders
        With Application.ActiveSheet
            .Cells(.Rows.Count, 1).End(xlUp).Offset(1, 0).Value = xSubFolder.Name
        End With
        ListFilesInFolder xSubFolder.Path
    Next xSubFolder
     
    Set xFolder = Nothing

End Sub

Public Sub TurnOffFunctionality()
    With Application
        lCalc = .Calculation: .Calculation = xlCalculationManual
        lStatusbar = .DisplayStatusBar: .DisplayStatusBar = False
        lEvent = .EnableEvents: .EnableEvents = False
        lScreen = .ScreenUpdating: .ScreenUpdating = False
    End With
End Sub
Public Sub TurnOnFunctionality()
    With Application
        .Calculation = lCalc
        .DisplayStatusBar = lStatusbar
        .EnableEvents = lEvent
        .ScreenUpdating = lScreen
    End With
End Sub

Und beobachte den Taskmanager, ob es Prozesse gibt (bspw: Virenscanner) die zum EXCEL-Prozess beachtlich CPU-Zeit für sich beanspruchen.