Common sync, without any ‘extras’ like smoothing etc. whatever sensitivity you find you prefer on hip, divide that number by 1.64 and that’s usually a good sensitivity for ADS.
I also use the advanced look with the pitch and yaws at max and everything else at zero.
Curve two clicks left of default, same for deadzone, threshold at default.
Apex legends is an inconsistent game tho, be ready to have different results between sessions