Yes, you can design clothes even if you do not know how to sew. Fashion design is a multi-disciplinary field that requires knowledge of various aspects of the fashion industry, including design, textiles, and production. While knowing how to sew can be helpful for a designer, it is not necessary to be able to design clothes.
There are a variety of tools and resources available to help those who do not know how to sew to create designs, including fashion design software like Prêt-à-Template, which offers a wide range of templates, design tools, and customization options. This software allows you to create detailed and polished designs without needing to know how to sew.
Additionally, you can also work with pattern makers and sample makers who can take your designs and create patterns and samples for you. This way you can focus on the creative part of the process, and have other professionals handle the technical aspects of creating the garments.