Error after upgrading to Drupal 10

Hello, 

After upgrading to Drupal 10 i got an Error in the following function:

Can you please help me ? 

public function saveappointmentuser(){

        @$user_current = \Drupal::currentUser()->id();
        @$user_info_current = \Drupal\user\Entity\User::load(\Drupal::currentUser()->id());
        $userID_current = $user_info_current->uid->value;

          $query = \Drupal::entityQuery('node');
        $query->accessCheck(TRUE);
          $query->condition('type', array('calendar_main'), 'IN');
          $query->condition('status', 1);
          $query->condition('uid', intval($_POST['owner']));
          $query->sort('nid', 'DESC');
          $entity_ids = $query->execute();

        $entity_ids = reset($entity_ids);

        if(isset($_POST['mykalendarpage']) && intval($_POST['mykalendarpage']) == 1){
            $name_appointment = 'Termin '.$this->counterappointments($entity_ids);
        }elseif(isset($_POST['mycreatepage']) && intval($_POST['mycreatepage']) == 1){
            $name_appointment = 'Termin '.$this->counterappointments($entity_ids);
        }else{
            $name_appointment = 'Buchung '.$this->counterappointments($entity_ids);
        }

        $appointment_data = array();
        $appointment_data['type'] = 'calendar_entries';
        $appointment_data['uid'] = intval($userID_current);
        $appointment_data['title'] = $name_appointment;
        $appointment_data['body'] = $_POST['text'];
        $appointment_data['field_calendar_selected_date'] = $_POST['date_format'];
        $appointment_data['field_calendar_selected_hour'] = $_POST['hour'];
        $appointment_data['field_calendar_id_assoc'] = intval($entity_ids);
        $appointment_data['field_calendar_entry_key'] = $_POST['date_format'].'>'.$_POST['hour'].'>'.$entity_ids;
        $appointment_data['field_calendar_entry_type'] = $_POST['type'];
        
        $appointment_data['status'] = 1;

        #$created_appointment = entity_create('node', $appointment_data);
        #$created_appointment->save();
        
        $created_appointment = \Drupal::entityTypeManager()->getStorage('node')->create($appointment_data);
        $created_appointment->save();
        $appointment_id = $created_appointment->uid->value;
        $load_calendar = Node::load(intval($entity_ids));

        $array_apppintments = array();
        foreach ($load_calendar->get('field_calendar_entry_assoc')->getValue() as $key => $value) {
            $appointmentload = Node::load(intval($value['target_id']));
            if(!is_object($appointmentload)){
                
            }else{
                $array_apppintments[] = $value['target_id'];
            }
        }
        $load_calendar->field_calendar_entry_assoc = $array_apppintments;
        $load_calendar->save();

        $load_calendar = Node::load(intval($entity_ids));
        $appointment_list_data = $load_calendar->get('field_calendar_entry_assoc')->getValue();

        if (empty($appointment_list_data)) {
            $load_calendar->field_calendar_entry_assoc[0] = $appointment_id;
            $load_calendar->save();
        } elseif(!empty($appointment_list_data)) {
            $appointment_count = count($appointment_list_data);
            $load_calendar->field_calendar_entry_assoc[$appointment_count] = $appointment_id;
            $load_calendar->save();
        }

        if(intval($userID_current) != intval($_POST['owner'])){

            //email send
            $custom_mails = new CemailController();

            $current_user =  \Drupal\user\Entity\User::load($userID_current);
            $owner_kalendar = \Drupal\user\Entity\User::load(intval($_POST['owner']));
            $custom_mails->userbookedmail($current_user);
            $custom_mails->teacherbookedmail($owner_kalendar);
            //email send

            //create chat

            //chat validation
              $query = \Drupal::entityQuery('node');
            $query->accessCheck(TRUE);
              $query->condition('type', array('chat_content'), 'IN');
              $query->condition('status', 1);
              $query->condition('field_chat_user_from', array($userID_current),"IN");
              $query->condition('field_chat_user_to', array($_POST['owner']),"IN");
              $query->sort('nid', 'DESC');
              $entity_ids = $query->execute();

              $query_second = \Drupal::entityQuery('node');
            $query_second->accessCheck(TRUE);
              $query_second->condition('type', array('chat_content'), 'IN');
              $query_second->condition('status', 1);
              $query_second->condition('field_chat_user_from', array($_POST['owner']),"IN");
              $query_second->condition('field_chat_user_to', array($userID_current),"IN");
              $query_second->sort('nid', 'DESC');
              $entity_ids_second = $query_second->execute();
            //chat validation

            if(!empty($entity_ids)){

                //create message

                $subject = 'User Comment ID '.htmlspecialchars($userID_current, ENT_QUOTES, 'UTF-8');
                $chatmessage = '<p>'.htmlspecialchars($_POST['text'], ENT_QUOTES, 'UTF-8').'</p>';

                $values = [
                    'entity_type' => 'node',
                    'entity_id'   => end($entity_ids),
                    'field_name'  => 'comment',
                    'uid' => $userID_current,
                    'comment_type' => 'comment',
                    'subject' => $subject,
                    'comment_body' => strip_tags($chatmessage),
                    'status' => 1
                  ];

                  $comment = Comment::create($values);
                  $comment->save();

                //create message

                /*echo $GLOBALS['base_url'].'/partner/profile/chat/'.$userID_current.'#'.end($entity_ids);
                die();*/

                $custom_url = $GLOBALS['base_url'].'/buchungerfolgreich';

                #drupal_set_message(t("Deine Buchung wurde erfolgreich durchgeführt."), 'status');
                echo $custom_url;

            }elseif(!empty($entity_ids_second)){

                //create message

                $subject = 'User Comment ID '.htmlspecialchars($userID_current, ENT_QUOTES, 'UTF-8');
                $chatmessage = '<p>'.htmlspecialchars($_POST['text'], ENT_QUOTES, 'UTF-8').'</p>';

                $values = [
                    'entity_type' => 'node',
                    'entity_id'   => end($entity_ids_second),
                    'field_name'  => 'comment',
                    'uid' => $userID_current,
                    'comment_type' => 'comment',
                    'subject' => $subject,
                    'comment_body' => strip_tags($chatmessage),
                    'status' => 1
                  ];

                  $comment = Comment::create($values);
                  $comment->save();

                //create message

/*                echo $GLOBALS['base_url'].'/partner/profile/chat/'.$userID_current.'#'.end($entity_ids_second);
                die();*/

                $custom_url = $GLOBALS['base_url'].'/buchungerfolgreich';
                #drupal_set_message(t("Deine Buchung wurde erfolgreich durchgeführt."), 'status');
                echo $custom_url;

            }else{
                $chatcreation = array();
                $chatcreation['type'] = 'chat_content';
                $chatcreation['uid'] = intval($userID_current);
                $chatcreation['title'] = "Chat between: ID-".$userID_current." and ID-".$_POST['owner'];
                $chatcreation['body'] = "Chat between: ID-".$userID_current." and ID-".$_POST['owner'];
                $chatcreation['field_chat_user_from'] = $userID_current;
                $chatcreation['field_chat_user_to'] = $_POST['owner'];
                $chatcreation['status'] = 1;

                        
                $created_chat = entity_create('node', $chatcreation);
                $created_chat->save();

                $chat_id = $created_chat->nid->value;

                //create message

                $subject = 'User Comment ID '.htmlspecialchars($userID_current, ENT_QUOTES, 'UTF-8');
                $chatmessage = '<p>'.htmlspecialchars($_POST['text'], ENT_QUOTES, 'UTF-8').'</p>';

                $values = [
                    'entity_type' => 'node',
                    'entity_id'   => $chat_id,
                    'field_name'  => 'comment',
                    'uid' => $userID_current,
                    'comment_type' => 'comment',
                    'subject' => $subject,
                    'comment_body' => strip_tags($chatmessage),
                    'status' => 1
                  ];

                  $comment = Comment::create($values);
                  $comment->save();

                //create message
            
            }

            //create chat

            $custom_url = $GLOBALS['base_url'].'/buchungerfolgreich';
            #drupal_set_message(t("Deine Buchung wurde erfolgreich durchgeführt."), 'status');
            echo $custom_url;

        }else{
            echo 'ok';
        }
        die();
    }