There is physically only one fan in the I-Pace. So changing speed of fan, if would affect all zones. However please keep in mind, that Climate system is controlling amount of air being blown to each zone/seat also by opening/closing flaps.
By the way...
You can have multiple levels of AUTO climate (this is generic to ALL cars, not only Jaguar):
Full AUTO (controlling temp, fan speed and direction of air distribution, A/C is ON)
Semi AUTO (either fan speed or direction is selected by user or A/C is OFF) - system is trying to use the other factors to manage pre-set temp
Mostly manual (fan speed and direction are set by user, A/C is switched OFF) - system is trying to maintain set temperature by just switching ON or OFF heater.
In fact you can not go to full manual...