As of the moment, there isn't an integrated way to update the invoice in your view once the customer has received it. Or even if the invoice has been opened from the email.
With this, let's consider letting our product developers know about your request by following the steps below:
Go to the Gear icon.
Under PROFILE, select Feedback.
Describe your request in a few words. Say - A Seen status after the customer confirmed the sent invoice.