How to remove the separator between values of a multi value field in a Views result?
Finally, I found the solution. I'm not sure if is the best, but it works.

function MY_THEME_preprocess_views_view_field(&amp;$variables){
  $view = $variables['view'];

  if ($view-&gt;id() == 'VIEW_ID'){
    $output = str_replace(',', '', $variables['output']);
    $variables['output'] = \Drupal\views\Render\ViewsRenderPipelineMarkup::create($output);
  }
}