How to track invoices that are "Marked as Sent"?

How to track invoices that are "Marked as Sent"?

We have a problem where some invoices are automatically "Marked as Sent by Mike" when we look in the invoice history, and noticed that these invoices aren't actually being sent to the customer. We don't know of a way to track these invoices that are Marked as Sent, so we are looking into creating a Flow to detect this but there isn't a trigger specifically for when it is Marked as Sent.