Does the GPSR also apply to sole traders and small online shops?

Yes, without exception. Verordnung (EU) 2023/988 contains no exemption based on turnover or business size. Whether you are a wholesaler or a sole trader running an Etsy or Shopify shop: once you offer physical consumer products in the EU, the disclosure obligations under Artikel 19 apply in full. Marketplace sellers on Amazon or eBay are also covered — the platforms tightened their requirements from December 2024 and in some cases automatically block incomplete listings. There is no legal basis for arguing you are "too small for this".