There are many methods, but I will mention few as below:

First Method (Redirect using site cookie, function and htaccess):

1. Add below constants to wp-config.php file:
   

   define('WP_ADMIN_DIR', 'secret-folder');
   define( 'ADMIN_COOKIE_PATH', SITECOOKIEPATH . WP_ADMIN_DIR);

    

2. Add below snippet in function.php file of your active theme

   add_filter('site_url', 'wpadmin_filter', 10, 3);
   function wpadmin_filter( $url, $path, $orig_scheme ) {
       $old = array( "/(wp-admin)/");
       $admin_dir = WP_ADMIN_DIR;
          $new = array($admin_dir);
       return preg_replace( $old, $new, $url, 1);
   }

3. Add below lines to .htaccess file

   RewriteRule ^secret-folder/(.*) wp-admin/$1?%{QUERY_STRING} [L]

Second Method (Rename wp-login with new file like new-secret-login-file):

1. Rename wp-login.php with new file like new-secret-login-file.php in the root admin folder.
2. Open the new-secret-login-file.php and find and replace every instance of "wp-login.php" in the file – then replace it with your new file name as new-secret-login-file.php.
3. Now you should be able to log in by navigating to your new URL. In our case, it’s domain/new-secret-login-file.php.
   

Note: If any HTTP/HTTPS requests to the /wp-login.php, or /wp-admin, directories will lead visitors to a 404 not-found page.

Third Method (Protect wp-login.php With a Cookie and .htaccess):

1. Add this code into your .htaccess file in the root folder.

   <IfModule mod_rewrite.c>
   RewriteEngine On
   RewriteBase /
   RewriteCond %{HTTP_COOKIE} !^.*wp\-connect=2917998723.*$ [NC]
   RewriteRule wp-login.php - [F]
   </IfModule>

2. Create a new login page for cookie like new-secret-login-page.php and ad below code:

   <?php
   setcookie("wp-connect", 2917998723);
   header("Location: wp-login.php");

    

Note: Please remember, Admins need to first go to domain/wp-connect.php to access wp-login.php