If you've forgotten your Hide Backend URL, you can add the code below into the wp-config.php file anywhere as long as it is between the first line ( <?php ) and the line that says / That's all, stop editing. Happy Blogging / to temporarily disable all features so you can log in.
Once you're back in, you can visit Security -> Settings -> Advanced -> Hide Backend to find your login slug. Be sure to remove the code from the wp-config.php file or set it to false to reactivate the features.
If needed, you can see how to edit the wp-config.php file in this article.