Hello @khawk,
As of the moment, there isn't an integrated way to let a user only create invoices. This is because once you let a user access your account with access to your customers, he/she can access all tasks related to customer transactions.
That being said, here's an article you can read to learn more about the different access and permissions you can give to a user: Learn about the different user types and levels of access in QuickBooks Online.
Additionally, I've also included this helpful article to identify how many users you can invite with your current subscription: Learn about usage limits and what your best options are if you reach one.
If you have any other questions, please let me know by leaving any comments below. I'll be here to assist you. Stay safe and well!
