Understand.
This borad is not Nucleo-F103RB, this is BluePhill ( Bluepill board support for Mbed OS 6 - Custom and community boards - Arm Mbed OS support forum) board and it changes the game a little bit.
The default Mbed console (STDIO) which is used for printf is set to PA_2 and PA_3. So, so you won’t see it until you connect a serial converter to those pins.
I am not sure, about the content in your terminal, but it seems like the comunication between BluePhill and A9G. The Bluephill sent the AT command and A9G responded with OK and that is correct.
BR, Jan