Does a Branch generated QR code have an expiration date?

No, QR codes do not have an expiration date. The QR code has a Short Link behind it. As long as the Short Link is active, the QR code will continue to work. Short Links will always be active if not deleted or archived. However, if you change the link domain (***.app.link) of your Branch app, all Short Links and the QR codes created with the old domain will stop working.