Hey @Erik-Gilpa,
Got it! Since it sounds like the shop is connected to Klaviyo via API (custom integration) without passing along an Ordered Product event, then it’s to be expected that you aren’t seeing the "Best-selling products" and "Both best-selling and most viewed products" options.
As highlighted in the previously mentioned Integrate a platform without a pre-built Klaviyo integration Developer guide:
For each line item, you should also make a Track request payload to generate an Ordered Product event. This metric is useful if you plan to create any filters or triggers based on product-specific information (as opposed to an order as a whole) that isn't "top-level" for the Placed Order metric. This metric is also used in conjunction with your Catalog Feed in order to enable personalized recommendations and in the benchmarks feature to calculate average item value and average cart size
If you did want to order your dynamic product feed by best-selling products, I would advise reaching out and working alongside your developer to implement this change. If you need more hands on assistance or an introduction to a developer, I would recommend reaching out and speaking to some of our wonderful Klaviyo Partners.
David