I recently came from the US and while the airline checked for the vaccination, it seemed they were more interested that the name matched. The Timatic site does not say anything about a QR code, only that the vaccination certificate shows that they were fully vaccinated at least 14 days before departure from the first embarkation point. The certificate must be in English, Portuguese or Spanish. This was also checked on arrival, again, that name matched. In neither case was anything used to read a QR code. Also remember that the Brazilian health statement needs to be done. It is found here: https://formulario.anvisa.gov.br/ Check with the airline, as they won't let you board without the correct documentation.