WooCommerce uses custom post types, so if the client hasn’t actually created Pages/Posts all the content will be under labels like “Products.” I would start by either determining whether there’s an XML sitemap – if they have Yoast SEO installed, you’ll see an “SEO” menu where you can check “XML Sitemaps” and generate one if there isn’t one already, so you can see all the content WordPress is aware of – or if there is no XML sitemap, do a Google site: search and see what they have indexed. If everything is under sitename.com/products/ or sitename.com/shop/ or anything similar, it’s likely they have only published Product content rather than Pages or Posts.
Once you have the list of URLs on the website you should be able to determine which URLs come from which post types. It would be extremely unusual for a site to “hide” Pages and Posts – it’s more likely there just aren’t any, other than the About page you found.