Customers now get the Confirmed email only once you actually confirm their reservation. Before, creating an invoice on a Pending reservation could send the confirmation early, even though you hadn't confirmed it yet. Now a pending reservation with an invoice gets the thank-you email and the invoice, and the thank-you email mentions that the invoice was sent separately.
On a pending reservation, the button now reads Confirm Reservation when an invoice has already gone out, so confirming won't create or email a second invoice. If there's no open or paid invoice yet, you'll see Confirm & Send Invoice instead. Draft or voided invoices don't count as already sent.
When you confirm, the confirmation email is recorded in the reservation's activity log right away, and the messages you see after confirming now tell you whether an email actually went out. There's nothing to change on your end.