WordPress redirects to login page when I enter url.com/index.php

There are several ways to fix your issue.

1. Add Codes to wp-config.php

   Add these lines in wp-config.php file:

   define('WP_HOME','http://example.com');
   define('WP_SITEURL','http://example.com');
   

2. Clear Cache

   Make sure to clear the cache from your browser, as well as cache
   plugins. You can also try adding this line to wp-config.php file:

   define( 'WP_CACHE', false );
   

3. Identify the Defective Plugins

   May be, you are using a defective plugin that is causing the issue.
   Try deactivating all the plugins in your site. Then activate one by
   one to find the defective one.