Recently bought a thermometer/hygrometer. It said the external sensor is calibrated for -40 to 60°C (values might be a bit off but in that ballpark) while the internal one is calibrated for -20 to 100 (again might be a bit off).

There was a 1 star review of someone using it in his sauna (so around 100°C) and seeing a big discrepancy between data from the two sensors so "it clearly can't be very accurate".