I think people already know the answer, but for the newbie...

It is needed to set USART3's TX & rX at PD8 and PD9. As a default, USART3's TX and RX would be PB10 and PB11. So we need to change ports and pins manually.

For more information, you can find schematics at CAD resource page in ST.com: https://www.st.com/en/evaluation-tools/nucleo-f767zi.html#cad-resources