You need Point of Sale once you integrate Shopify into QuickBooks Online since we're also unable to use POS with QBO.
If you want to integrate POS into QBO, you can look for a third-party application that works best for your program. You can use customer reviews to help you decide which app best suits your business type and needs.
You can also follow the steps below to search for the app:
Go to the Apps menu from the left pane.
Enter a keyword in the search bar, like "point of sale" or click the Browse category button.