theming – Why is my template suggestion not called (the return)?

I have seen many questions like this ones and I have tried all the solutions…

Here is my setup:

1-I have a custom entity with the id defined as follow:

 * @ContentEntityType(
 *   id = "bank_operation",
 *   label = @Translation("Bank Operation"),

2- My hook_theme():

function bank_operation_theme() {
  return (
    'bank_operation' => (
      'render element' => 'elements',
     ),
  );
}

3- My hook_theme_suggestions_HOOK()

function bank_operation_theme_suggestions_bank_operation(array $variables) {
  $suggestions = ();
  $sanitized_view_mode = strtr($variables('elements')('#view_mode'), '.', '_');
  $suggestions() = 'bank_operation__' . $sanitized_view_mode;
  return $suggestions;
}

4- My Route to display the entity with a “receipt” view mode

entity.bank_operation.receipt:
  path: '/bank_operation/receipt/{bank_operation}'
  defaults:
    _entity_view: bank_operation.receipt
    _title: 'Receipt'
  requirements:
    _entity_access: 'bank_operation.view'

5-My twig files:

modules/custom/bank_operation/templates/bank-operation.html.twig
modules/custom/bank_operation/templates/bank-operation--receipt.html.twig

Result: Everything works fine :

receipt view mode is used

-suggestions seems to be correctly added:

<!-- THEME HOOK: 'bank_operation' -->
<!-- FILE NAME SUGGESTIONS:
   x bank-operation.html.twig
   * bank-operation--receipt.html.twig
   x bank-operation.html.twig
-->
<!-- BEGIN OUTPUT from 'modules/custom/bank_operation/templates/bank-operation.html.twig' -->

Except that bank-operation--receipt.html.twig is not called

I have tried all combinations of file name/suggestions/base hook name/… without any success

I have added all the possible twig file name in my templates folder (with or without dash)

I have the feeling that the problem is coming from the fact that the ID of my entity have an underscore in its name…