The draft status will only operate before submitting the purchase order for approval, Thus if you want to create purchase order with a draft status then you don;t submit the PO for approval. Once the PO gets submitted the status would be changing to ‘In review’ status.
This isn’t possible without modifications. If I remember correctly, purchase orders in the “draft” status don’t have any inventory transactions. It’s not until they get through the workflow that the inventory transaction is created.
As master planning relies on these inventory transactions in order to properly calculate net requirements, it forces the status to be past draft after firming.