Sure! When you click on New creative button under Creatives section, there is Skip button. If you're not willing to promote any product in particular, you can click Skip button in the top-right corner and proceed with simply a creative creation.

In this way, you can generate the ad creative without linking it to a specific product.

Of course. If there's no product you'd like to promote in the list, add a new product by clicking Add new product button.