How to use hook_views to add calculation to a field?
Finally, after some (!!) digging, I did it in assoc_views_post_execute

function assoc_views_post_execute(ViewExecutable $view)
{
  switch ($view-&gt;id()) {
    case 'assoc_persons':
      if ($view-&gt;current_display == 'page_1') {
        $database = \Drupal::database();
        foreach ($view-&gt;result as $key =&gt; $value) {
          $person = $value-&gt;_entity-&gt;get('id')-&gt;value;
          $solde = $value-&gt;_entity-&gt;get('balance')-&gt;value;

          some code to calculate credit with database query
          $credit = $result[0]-&gt;credit;

          some code to calculate debit with database query
          $debit = $result[0]-&gt;debit;

          $solde = $solde + $credit - $debit;
          $value-&gt;_entity-&gt;set('balance', $solde);
        }
      }
      break;
    default:

  }
}