I'm delighted to see you here joining the thread and sharing details of your concern. I understand you want to use the NEW invoice format but still delete time without unlinking it. Allow me to chime in and impart insight that could help you get through this.

In the new format of QuickBooks Online, if you want to delete a line item from an invoice without unlinking the billed time, you can instead remove Billable time from the linked transactions. I will attach screenshots for better reference. 

From the invoice page, if you click the trash icon beside the line item, you will receive a prompt stating that if you delete the line, you will have to unlink the Time Activity, which will remove all other lines associated with this transaction.

Otherwise, removing the Billable time will let you keep the Time Entry. Here's how:

1. From the transaction page, select the Linked transactions under the INVOICE.
2. Click Remove on the Billable time.
   
   
    
3. A prompt will appear to save the transaction. Pick Yes.
   
   
    
4. Select Save and Close.

You can then check the Time entry you kept even after unlinking the transaction.

I'm adding these articles you can use in the future:

• Delete customers with unbilled charges in QuickBooks Online.
• Remove a billable expense charge in QuickBooks Online.

If you have any further questions or need additional assistance with managing billable expenses, feel free to post here again. I will always be around to help. That's it for now. Stay safe!