I agree, I think the BIOS-level fan controls on Asus/Gigabyte/AsRock boards would do what you need. Most PWM fans don't actually spin once the PWM signal is below....20%(?) so it would just be a matter of satisfying that setting. Of course, setting a PWM signal on that's below the fan's threshold could result in unwanted PWM whine that could be worse than running the fan at minimum RPM, so 0% is ideal.
No guarantees, my mobos are too old to have the level of fan control granularity that today's mobos offer. But anyone with a recent board should be able to test it and report in.
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