Hi masoodnevisi,
EULER_SENSOR_ID this github example, the definition is the same as orientation. #define EULER_SENSOR_ID BHY2_SENSOR_ID_ORI_WU https://github.com/BoschSensortec/BHY2-Sensor-API/blob/master/examples/euler/euler.c
Orientation will enable 9doF algorithm with magnetometer to output euler angles. If you don't use BMM150 magnetometer in our hardware, you could get quaternions output data, and convert it to euler angles.
The current firmware does not support using orientation without a magnetometer sensor.
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