Hi there, @andrew-hall1.
You have the option to enter multiple emails in your customer's profile or invoices. Any attached email will receive the invoice once sent. Make sure that the email addresses are separated with commas (,).
Please check out the sample snips attached below on how add them on your customers profile and on sales forms:
To give you more details about adding customer's and emailing forms in QuickBooks Online, please see these resources:
Know that my doors are always open to help if there's anything else you need. Thanks for coming, and have a good one!
As mentioned above, for individual customers you are able to add in a contact email that will pre-fill the Invoice once you create it. At this point you will have to add in manually the CC or BCC details to the invoice.
I agree it would be good to see this automated in the future, please use the steps below to share this feedback with us.