Since the entire top bar is the main navigation, there isn’t a super easy way to do this.
You could try a function like this:
add_filter( 'wp_nav_menu_items', function( $nav, $args ) {
if ( $args->theme_location == 'primary' ) {
$text = 'Your custom text here.';
return $nav . '<li class="custom-text"><a href="#">' . $text . '</a></li>';
}
return $nav;
}, 20, 2 );
Adding PHP: https://docs.generatepress.com/article/adding-php/
Let me know 🙂