The datasheet for the STM32G431 (DS12589 Rev 2) shows that the I2C3 peripheral is available on pins PC8 and PC9, but on page 206 of AN2606 Rev 42 it says that the bootloader is using PC6 and PC7 for I2C3. Since STM32CubeMX 5.5.0 agrees with the datasheet about the location of I2C3, I assume that AN2606 is wrong and needs to be corrected.
A quick comparison of the STM32G473 datasheet with AN2606 shows that there are probably STM32G473 errors in AN2606 too.
galen
