On Shopify, you can sell products and services (digital and physical), so long as they comply with Shopify’s values and are not illegal.
Shopify’s Acceptable Use Policy says they believe in a “free and open exchange of ideas and products.” Stating this free and open exchange is a key tenet of commerce, however, there “are some activities that are incompatible with Shopify’s mission to make commerce better for everyone.”
Those activities include things like child abuse, illegal substances, and services from terrorist organizations. If you’re trying to monetize say, your templated social media strategies or your Grandma’s home-baked pies, you’re likely good. Unless Grandma uses some wild ingredients.