Hi,
According to the wiki, r4s has i2c bus at 2x5 pin header:

4 GPIO4_C0/I2C3_SDA(3V)
6 GPIO4_C1/I2C3_SCL(3V)

However, on a friendly core the board with i2cdetect shows only buses 0-2,4,7,9.
And does not see the device connected to pins.

How should I deal with 3rd i2c bus?

Thanks.