We are working with the NanoPC-T4 and NanoPi NEO4 (pretty similar boards). We are running FriendlyCore, and we are able to use the I2C bus on pins 3 and 5 just fine via the exposed /dev/i2c-2 device. Both boards state that pin 8 is "GPIO4_C1/I2C3_SCL", and pin 10 is "GPIO4_C0/I2C3_SDA...