I confirm you that also for ISM330 the INTERNAL_FREQ_FINE is factory calibrated.
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Update : I found a post from Wellett "IIS3DWB - ODR Accuracy" where the same question is asked relating to the IIS3DWB. The response from Federica Bossi says it is set at the factory.
I presume this would be similar for the ISM330.
If this is the case, then since INTERNAL_FREQ_FINE is only set once, that means it does not change with temperature or age of the device.
Presuming 25 Celsius is the measurement point for the standard (based on Federica's response), the accuracy can be +/- 0.5% at 85 C and +/- 0.65% at -40 C.
I confirm you that also for ISM330 the INTERNAL_FREQ_FINE is factory calibrated.
In order to give better visibility on the answered topics, please click on 'Best answer' on the reply which solved your issue or answered your question.