I am trying to create table on plugin activation, I tried making the same function inside the class and calling it from the constructor, and I tried calling it outside the class and finally i tried to make another php file for calling it using the register_activation_hook, but nothing worked

plugin-code:

<?php
/**
*@package pageauthors
**/

/** 
* Plugin Name: Page Authors
* Plugin URI: https://www.localhost.com/plugin
* Description: Allows you to add multiple authors to your wordpress post.
* Version: 1.0.0 
* Author: Raphael Eid.
* Author URI: https://www.localhost.com/
* License: GPL v2 or Later 
* Text Domain: PageAuthors
*/

$db = mysqli_connect('localhost','x','x','x');
//We can use require_once('../../../wp-config.php');
//mysql_connect(DB_HOST, DB_USER, DB_PASSWORD);

defined('ABSPATH') or die('Error my friend');

class pageauthors{

    function register(){
        //Call the Scripts
        add_action('admin_enqueue_scripts', array($this, 'enqueue'));

        //Create in the admin function
        add_action('admin_menu', array($this, 'add_admin_pages'));
    }   
    
    public function add_admin_pages(){
        //add_menu_page( string $page_title, string $menu_title, string $capability, string $menu_slug, callable $function = '', string $icon_url="", int $position = null )
        add_menu_page('Add Author', 'Add Author', 'manage_options', 'raphaelprefix_plugin', array($this, 'admin_index'), 'dashicons-insert', 110);
    }

    public function admin_index(){
        define( 'MY_PLUGIN_PATH', plugin_dir_path( __FILE__ ) );
        include( MY_PLUGIN_PATH . 'templates/index.php');
        // include( MY_PLUGIN_PATH . 'index.php');
        include( MY_PLUGIN_PATH . 'templates/showAuthors.php');
        // require_once plugin_dir_path(__FILE__) . 'templates/index.php';
    }    

    function deactivate(){
        global $wpdb;
        $table_name = $wpdb->prefix . 'postsauthors';
        $sql = "DROP TABLE IF EXISTS $table_name";
        $wpdb->query($sql);
        delete_option("my_plugin_db_version");
    }

    function enqueue(){
        //Here we can enqueue and we should create the assets (css and js)
        wp_enqueue_style('mypluginstyle', plugins_url('/assets/mystyle.css', __FILE__) );
        wp_enqueue_script('mypluginstyle', plugins_url('/assets/mystyle.js', __FILE__) );
    }

}

if(class_exists('pageauthors')){
    $raphplugin = new pageauthors();
    $raphplugin->register();
    // $raphplugin->activate();
    $raphplugin->deactivate();

}

function installer(){
    include('installer.php');
}

//Activate - Register Activation Hook(__FILE__, array($instance, function))
register_activation_hook(__FILE__, 'installer');

//Deactivate - Register Deactivation Hook(__FILE__, array($instance, function))
register_deactivation_hook(__FILE__, array($raphplugin, 'deactivate') );

?>

installer.php

<?php
$db = mysqli_connect('localhost','x','x','x');
    global $wpdb;
    require_once(ABSPATH . 'wp-admin/includes/upgrade.php');

    if (count($wpdb->get_var('SHOW TABLES LIKE "wp_postsauthors"')) == 0){

        $sql = "CREATE TABLE `wp_postsauthors` 
        ( `ID` INT(200) NOT NULL AUTO_INCREMENT , `post_ID` INT(200) NOT NULL , 
        `author_name` VARCHAR(200) NOT NULL , `title` VARCHAR(200) NOT NULL , 
        `description` VARCHAR(200) NOT NULL , PRIMARY KEY (`ID`)) ENGINE = InnoDB;";

dbDelta($sql);

}

Nothing is working even tho I am typing everything correctly