There error indicated is error: ambiguating new declaration of 'void sleep(uint32_t)'. This means the sleep() function in bsec_iot_example has the same name as a function in the ESP32 toolchain, which is not permitted. This could be solvable by renaming the sleep function in bsec_iot_example, for example into "delay_ms" or similar. Note that if you are using the Arduino IDE, we also have an Arduino library available for the BME680+BSEC.
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