The Mac Mini and laptops use external sensors as well as S.M.A.R.T. services within the drive. You don’t need any extra sensor unit.
At this point SMC services has either lost access to the needed sensor or a sensor was damaged. Your system is in CPU safe mode which ramps up the fan and lowers the CPU’s clocking to protect your system. So trying to offset this is not the correct direction.
You should run diagnostics to identify the sensor. Restart your system and press the ***D*** key on your keyboard.
Reference: [https://support.apple.com/en-us/HT201255|Mac startup key combinations]