Scenario: User needs to not create PO for a dropship item with all dropship item in the SO having same preferred vendor.
Solution:
Go to Transaction> Sales> Enter sales orders.
Create sales order with all items having same preferred vendor and make create PO column blank for the specific item for which the PO doesn’t needs to be created. Also enter the mandatory fields and click save.
PO created for only the other two item(based on screenshots)
Note: If the dropship item excluded from PO creation is having quantity in stock, then it will be fetched from the stock.