Merchant wants customers to buy the in stock and preorder for the same product in 1 order

If merchant has 2 units left and this product is selected as preorder, the customer should be able to buy more than 2 units, the 2 units should come in as regular and the rest should be preorder
Link: https://app.crisp.chat/website/2911cad6-d4a1-461c-9004-f4e58a19b68a/inbox/session_245a5e25-8e2a-47d4-ba3b-0be6264918be