Save default options as an array of options and display in REST API

I solved the issue thanks to this answer: Serialized settings in rest api.

I was able to store all the options as a json object:

/**
 * Create plugin options schema as an object and prepare it for the rest api. 
 * WP >=5.3
 */
function my_register_settings() {

    $general_options = [
        'show_in_rest' => [
            'schema' => [
                'type'       => 'object',
                'properties' => [
                    'is_show_post'     => [
                        'type'    => 'string',
                        'default' => 'true',
                    ],
                    'is_show_page'     => [
                        'type'    => 'string',
                        'default' => 'true',
                    ],
                    'is_show_cpt'      => [
                        'type'    => 'string',
                        'default' => '',
                    ],
                    'featured_post_id' => [
                        'type'    => 'string',
                        'default' => '',
                    ],
                ],
            ],
        ],
    ];

    // register plugin options as an object
    register_setting(
        'awg_settings',
        'awg_options',
        $general_options
    );

}

add_action( 'init', 'my_register_settings' );