STM32L4A6 USART port selection for bootloader?

[programmer131]

Bootloader only responding on PC10 and PC11, but not on PA2,PA3,

how to select a particular UART port for bootloader?

 

[Tesla DeLorean]

It is typically looking for signal transitions on multiple pins, first one to see traffic wins the race.

Make sure the other RX pins are not noisy, ie data from a GPS/GNSS receiver that squawks at startup.