Hi @Tristar
have you tried to run the I2C scanner program? This should give you an idea of what's connected to the I2C bus.
https://github.com/m5stack/M5Stack/tree/master/examples/Advanced/I2C_Tester
For instance MPU6886 is at address 0x68 and when you read register 117 - WHO_AM_I you should get 0x19.
Felix