Usually they design what they call, autodetect headers, these are 4pin headers that can do voltage control (3pin) or PWM control (4pin), this headers will detect if you plugged a 4pin or 3pin and react accordingly, but usually asrock only includes 2 headers like this (in some cases only 1, on value mobos), the rest of the 4pin headers (that are not autodetect) are only PWM control, and most cases the 3pin headers are not controllable, like pure 12V header.

One last comment, in the past the Autodetect headers were more commonly the CPU_FAN1 and CHA_FAN1 (in some mobos CPU_FAN2), recently they steered away from this practice and now on Z370 there are no autodetect headers, but switchable on bios, but the usual header that you would think as above are not switchable, for example on the Z370 Taichi only ones that can do 3pin voltage are CPU_OPT and CHA_FAN3, meaning that CPU_FAN1, CHA_FAN1, and CHA_FAN2 are pure 4pin voltage controlled.  But I don't believe this is the case for your motherboard, i think yours are still when ASRock did do the autodetect headers.