I am in the same situation.  I need the price rules to discount each line item.  Just using the discount on the total invoice does not work.  I was told QB will not change this. 

Features currently unavailable in the new experience

The following classic invoice features are currently unavailable in the new experience:

• Reference links displaying matched online transactions
• Price Rules (You can create and manage Price Rules, but the new invoice experience currently doesn't support price rules applied on invoices.)
• Add previous attachments
• "Add all" for suggested transactions
• Billable Mileage Tracking
• Copy PO to invoice

Many businesses are complaining of this and QB needs to listen to their customers. We are paying thousands of dollars for software that doesn't work as it should.