It is possible to test sent for processing status with any open banking payment method in the demo environment. Please check how to test open banking from here.
When initiating payment, set the amount to 33 EUR and go through the payment flow like normally. After confirming the payment, it will stay in sent for processing status for 30 seconds and then it will go to final status, normally it will be settled.
*Setting the amount to 33 EUR does not affect card payment flow.