In most cases, the demo process cannot select the default Shop pages such as Shop, Cart, Checkout and My Account page.
You need to go to WooCommerce -> Settings -> Product tab to choose Shop page
Go to WooCommerce -> Settings -> Advanced tab to choose Cart, My Account and Checkout page
To make sure the permalink works well, please go to Settings -> Permalink,
In Common setting, select Post name
In Product Permalink, select Default