Hello @dailletaille
glad it worked. Thank you for reporting back. My guess is something's wrong with the UIFlow block - it would not be the first time.
BTW: the GPIO output is not directly connected to the motor; there is a MOSFET in between to translate between 3.3 V and 5 V. But 0.5 V is definitely too low for it to fully switch on. See schematic here.
Thanks
Felix