Best Sellers can be added to your sort order configuration from the Magento admin in Stores > Algolia Search > Instant Search Results Page > Sorts.
Click “Add” to add a new row and select the attribute
ordered_qty with the Sort direction as Descending.
Please note that adding this sort order adds
total_ordered attributes to your product objects, aggregated from the
sales_order_item table. This can potentially increase your indexing time.