The best way to create a login page in WordPress without using a plugin to the site is to create a custom page with the custom template and use WP_login_form() function to publish the plugin form on the page
<form action="<?php the_permalink(); ?>" method="post" class="sign-in">
<p>
<label for="user-name"><?php _e('Username'); ?></label><br />
<input type="text" name="user-name" id="user-name" value="<?php echo wp_specialchars( $_POST['user-name'], 1 ); ?>" />
</p>
<p>
<label for="password"><?php _e('Password'); ?></label><br />
<input type="password" name="password" id="password" />
</p>
<p>
<input type="submit" name="submit" value="<?php _e('Log in'); ?>" id = "yellow-button" />
<input type="hidden" name="action" value="log-in" />
</p>
</form>see https://wphow.co/kb/how-to-add-a-login-page-in-wordpress/
