Glad to see you here in the Community space. I’d like to address your concern about creating a CSV file to import multiple invoices all at once into QuickBooks Online.
While CSV is one of the common file format used to import transactions to QuickBooks, only Customers, Vendors, Accounts, Products and Services can be imported. I’d suggest sharing us your opinion and let our Developers know what you liked and what we can improve to make it better.
You may also want to check out other 3rd party apps that can integrate and import invoice transactions in CSV file. I recommend clicking Apps in the Dashboard and type Import Transactions in the search field.
While some apps have a fee, there are also some applications you could use for free. All of these apps are available in the App Center in QuickBooks Online.