Can't see the settings page custom fields under Media menu

I've created a settings page and some custom fields for it, and I wanted to show this page under the Media menu as a submenu.

function add_my_settings_page( $settings_pages ) {
    $settings_pages[] = [
        'id'          => 'my_settings_page',
        'option_name' => 'my_settings_page',
        'menu_title'  => esc_html( 'My Settings Page' ),
        'position'    => 25,
        'parent'      => 'upload.php',
        'capability'  => 'upload_files',
        'style'       => 'no-boxes',
        'columns'     => 1,
        'icon_url'    => 'dashicons-admin-generic',
    ];
    return $settings_pages;
}
add_filter( 'mb_settings_pages', 'add_my_settings_page' );

function add_my_settings_page_fields( $meta_boxes ) {
    $meta_boxes[] = [
        'title'          => 'my_settings_page_fields',
        'id'             => 'my_settings_page_fields',
        'settings_pages' => ['my_settings_page'],
        'fields'         => [
            [
                'name' => 'Upload Video',
                'id'   => 'upload_video',
                'type' => 'file',
            ],
        ],
    ];
    return $meta_boxes;
}
add_filter( 'rwmb_meta_boxes', 'add_my_settings_page_fields' );

I can see the submenu of that page, but when I access it, I only see the title of the settings page and the save button. All the other custom fields are not being loaded!

The strange thing is that when I change the parent to any other menu except upload.php, or set it as a main menu, I'm then able to see the custom fields.