I looked into it again. Seems like you need to make an extra macro to enable gcode control.
macro:
[gcode_macro M141]
gcode:
{% set s = params.S|default(0)|float %}
SET_TEMPERATURE_FAN_TARGET temperature_fan=“exhaust_fan” target={s}
I got it from Chamber Temperature & Exhaust Fan | Voron Documentation but had to change “chamber“ to “exhaust_fan“
Now I can change the target via M141 s60 for example to set it at 60C