I would recommend NOT forcing HTTPS quite yet. Instead, remove all that stuff in wp-config.php and in the .htaccess. Then, login to WordPress making sure you’re using the HTTPS link.
If you can login, then you now know you can login as both HTTP and HTTPS. Then, you can force HTTPS. If you can login at HTTP but not HTTPS, then I would recommend changing your SALT keys in your wp-config.php file (https://api.wordpress.org/secret-key/1.1/salt/) and visiting the site again in private browsing mode.
SSL certificates get cached by your browser and changing the SALT keys can often force these pesky caches to update.