How would a Business Practitioner ensure that only orders with a subtotal greater than $50...

According to the Adobe Commerce Merchant Documentation, you can set a minimum order amount that customers must meet or exceed to complete an order by enabling the Minimum Order Amount option and entering the Minimum Amount in the Stores > Configuration > Sales > Minimum Order Amount section.

References: https://docs.magento.com/user-guide/sales/minimum-order-amount.html