Dim fileSaveName As String

    fileSaveName = Application.GetSaveAsFilename(fileFilter:="These two types only (*.txt;*.xls), *.txt;*.xls")

Private Sub CommandButton2_Click()
Dim fileSaveName As String
    
    If CheckBox5.Value = True Then 'Куда угодно
        
        fileSaveName = Application.GetSaveAsFilename _
            (fileFilter:="Файл (*.txt;*.xls), *.txt;*.xls")
       
        If fileSaveName <> "False" Then
            Select Case UCase(Right(fileSaveName,  3 ))
                Case "XLS"
                    Workbooks("имя книги, которую нужно сохранить").SaveAs Filename:=fileSaveName, FileFormat:=xlExcel9795
                Case "TXT"
                    Workbooks("имя книги, которую нужно сохранить").SaveAs Filename:=fileSaveName, FileFormat:=xlText
            End Select
        End If
    End If
End Sub