This happens because your AA is off, turning it on shall make the hairs look normal again, but the whole game will have a blurry look. The only way to improve hair's quality when AA is off is by using a high resolution quality, which even with a RTX you will lose a lot of performance. But if you want to turn your aa on again, change r.defaultfeature.antialiasing=2 and r.postprocessaaquality=3/4