Show all the data when filter is empty

Assuming that there is one column which contains non blank values. Let's assume this column is Region (Looks like your Numero client is one such column). Then you can use following code

let

  // ajout des paramètres de filtre                                                                                                                                                                                                                                       
  filtreRegion = f_Region,
  filtreSource = f_Source,
  filtreOperateur = f_Operateur,

  Source = Excel.CurrentWorkbook(){[Name = "tbl_region_source"]}[Content],
  #"Filtered lines" = Table.SelectRows(
    Source,
    each
      if f_Operateur = "or" then
        [Région] = f_Region or [Source] = f_Source
      else if f_Operateur = "and" then
        [Région] = f_Region and [Source] = f_Source
      else [Région]<>""
  ),
  removingDuplicate = Table.Distinct(#"Filtered lines")
in
  removingDuplicate

Now' let's assume that there is no such column. In this case, you can insert one Index column. Index column is always non blank and replace [Région]<>"" with [Index]<>""

Then you can remove the Index column after this step.