BIOS not detecting fan speed - getting fan error

ASUS TUF B450-Plus
CPU: Intel Core i5
CPU Cooler: Corsair Carbide Series
Since yesterday, the BIOS isn't picking up the CPU cooler at all. No RPM readings, nothing... even though I can physically see the fan spinning.
Everything was running smooth until yesterday when a Windows update ran, and then—poof—it just stopped working. Is there any chance a macOS-style OS update could mess with this, or is my cooler just kicking the bucket?

It had a 24-month warranty, but I'm sitting here at 25 months since I bought it. Great.

Can you actually see the fan speed for that cooler in the BIOS, or is it just missing once you're in macOS... or does it not show up in the BIOS at all?

Try resetting your BIOS—there’s a good chance that’s where the issue lies...

So, looks like my little brother totally botched it... there was absolutely zero fan speed being reported anywhere...
I mean, he had that 4-pin connector plugged into the chassis fan header, so the thing was physically spinning, but the system wasn't reading any RPM at all. It’s like a car speedometer stuck at zero while you're doing sixty.
I just swapped it over to the dedicated CPU header and now everything is running smooth as silk...