Redirect to a page for only logged in user

You can make more readable, like. Small notes at the code. As a hint, the template tag is_page() supports an array of values – is_page( [ 'login', 'register' ] ).

add_action( 'template_redirect', 'login_redirect' );
function login_redirect() {
    // If user is NOT logged in, doing nothing.
    if ( ! is_user_logged_in() ) {
        return;
    }
    // This OR (||) this. is_page supports an array of different values.
    if ( is_page( [ 'login', 'register' ] ) ) {
        wp_redirect ( site_url( '/account' ) );
        exit;
    }
}