Fatal error: Uncaught Error: Call to a member function on bool

I know this answer has been answered already but it seems like I couldn’t understand anything in my case (I’m still very new to web developing, learning frontend since this october and I jumped onto php at the start of this month).
My function is supposed to check if user is logged in and I couldn’t understand the answers I read for my problem cause it seems like in the answers I found, the functions weren’t custom? I might be wrong and I hope if I am, you can laugh about it.

So, to get a bit of context, I encounter this error when I try to call the function "check_logged_in()" in one of my controllers, this controller in question (it’s called Upload) extends the main Controller from my core folder (and I triple checked if my init file has required it so I can use it globally).
Then I call a custom function from the main controller to load models if needed (in this case, I need to load my user model to get access to the "check_logged_in()" function since it’s written there).
And this is where thing happen. I’ll provide a bit of code so you guys can understand what I’m saying.

The Upload controller

<?php

class Upload extends Controller
{
    function index()
    {
        header("location:" . ROOT . "upload/image");
        die;
    }
    function image()
    {
        $user = $this->loadModel("user");
        
        if(!$result = $user->check_logged_in()){
            header("location:" . ROOT . "login");
            die;
        }

        $data['page_title'] = "Upload";
        $this->view("upload", $data);
    }
}

The main Controller

<?php

class Controller
{
    protected function view($view, $data = [])
    {
        if (file_exists("../app/views/" . $view . ".php")) {
            include "../app/views/" . $view . ".php";
        } else {
            include "../app/views/404.php";
        }
    }
    protected function loadModel($model)
    {
        if (file_exists("../app/model/" . $model . ".php")) {
            include "../app/model/" . $model . ".php";
            return $model = new $model();
        }

        return false;
    }
}

And the bit of code from the user model that is called

<?php

class User
{
    function check_logged_in()
    {

        $DB = new Database();
        if (isset($_SESSION['user_url'])) {

            $arr['user_url'] = $_SESSION['user_url'];

            $query = "select * from users where url_address = :user_url limit 1";
            $data = $DB->read($query, $arr);
            if (is_array($data)) {
                //logged in
                $_SESSION['user_name'] = $data[0]->username;
                $_SESSION['user_url'] = $data[0]->url_address;

                return true;
            }
        }

        return false;
    }
}

Thanks in advance for your time mates, I hope my noob self is clear enough for you to understand ^^’

>Solution :

Checking for the correct value of the $user variable should fix the error.

...
    function image()
    {
        $user = $this->loadModel("user");
        
        if(!$user || !$user->check_logged_in()){ // Here
            header("location:" . ROOT . "login");
            die;
        }

        $data['page_title'] = "Upload";
...

Then on $user is false condition will be
!false || !false->check_logged_in() which will lead to true.

Otherwise on $user is User:
!(object User) || !(object User)->check_logged_in() will call User::check_logged_in() method.