designtopack/public/site/plugins/notifications/user-methods/send.php

<?php

return function ($group, $item) {
  foreach (kirby()->users()->not($this) as $otherUser) {
    try {
      $notifications = $otherUser->notifications()->isNotEmpty() 
          ? Yaml::decode($otherUser->notifications()->value())
          : [];          

      if (!isset($notifications[$group])) {
        $notifications[$group] = [];
      }
      
      $notifications[$group][$item->id()] = $item->toArray();

      $otherUser->update([
        'notifications' => $notifications
      ]);
    } catch (\Throwable $th) {
      throw new Exception("Error updating notifications: " . $th->getMessage() . ' line ' . $th->getLine(), 1);
    }
  }
};