But that the strange part, because we only program the ESP32 and if you look at the code, we use the mycropython machine library for the I2C with pins that are the one of the ESP32 (11 and 12) :
from machine import I2C
from machine import Pin
i2c = I2C(0, scl=Pin(12, Pin.OUT), sda=Pin(11, Pin.OUT))
On the STM32, the pins for I2C are not those. But are the I2C pins from both microcontrollers simply connected? But I thought the communication between them was through UART.