Render Elementor-styled content in WP-GraphQL

functions.php

add_action('graphql_register_types', function() {
        $post_types = WPGraphQL::$allowed_post_types;
        if (!empty($post_types) && is_array($post_types)) {
                foreach($post_types as $post_type) {
                        $post_type_object = get_post_type_object($post_type);
                        register_graphql_field($post_type_object->graphql_single_name, 'styledContent', [
                                'type' => 'String',
                                'description' => __('The styled elementor content of the page', 'cottontailpress-headless'),
                                'resolve' => function($post) {
                                        $content = '';
                                        if (class_exists('\Elementor\Plugin')) {
                                                error_log('class_exists');
                                                $plugin = \Elementor\Plugin::instance();
                                                $content = $plugin->frontend->get_builder_content($post->ID, true);
                                        }
                                        return $content;
                                }
                        ]);
                }
        }
});

replace
$post_types = WPGraphQL::$allowed_post_types; to $post_types = WPGraphQL::get_allowed_post_types();

Even better, replace it with WPGraphQL::get_allowed_post_types( 'objects' );

add_action( 'graphql_register_types', function() {
    $post_types = WPGraphQL::get_allowed_post_types( 'objects' );

    foreach( $post_types as $post_type_object ) {
        register_graphql_field(
            $post_type_object->graphql_single_name,
            'styledContent',
            [
                'type' => 'String',
                'description' => __('The styled elementor content of the page', 'my-translation-domain'),
                'resolve' => function( $post ) {
                    if ( class_exists('\Elementor\Plugin') ) {
                        return null;
                    }

                    $plugin    = \Elementor\Plugin::instance();
                    return $plugin->frontend->get_builder_content($post->ID, true) ?: null;
                },
            ]
        );
    }
} );