Hello there, @mot-alak.

 As mention by my colleague above, the option to display the open balance in the text along with the invoice number is unavailable in QuickBooks.

Please know that our developers are constantly working and considering new functions to be added to the system. This way, we will be able to coincide with our customers' needs and demands.

Also, you might want to check this article for reference in case you want to learn how to customize your invoice in QBO: Customise your invoices, quotes, and sales receipts in QuickBooks Online.

Please know that I'm just a post away should you need anything else. Wishing you a wonderful day!