Switch the URL of default login page with the URL of a custom login page

custom-login-page.php

<?php
/**
 * Set a custom login page
 *
 * @param string $url Default login URL
 * @param string $redirect Redirect URL on login
 * @param bool $force_reauth Whether to force reauthorization
 * @link https://developer.wordpress.org/reference/hooks/login_url/
 */
function frontend_login_url( $url, $redirect, $force_reauth ){
    $new_login_url = home_url( '/login-form/' );

    if ( !empty($redirect) ){
        $new_login_url = add_query_arg( 'redirect_to', urlencode( $redirect ), $new_login_url );
    }

    if ( $force_reauth ){
        $new_login_url = add_query_arg( 'reauth', '1', $new_login_url ) ;
    }
    return $new_login_url;
}
add_filter( 'login_url', 'frontend_login_url', 10, 3 );