This device is not spec’ to operate a variable fan motor. You’ll either burn out the fan motor or the switch and may cause a fire.
This is true of pretty much all dimmer switches intended for lighting. The physics are different for a motor.
You need to select a device which is specifically designed to operate a variable speed fan motor. Quite a few people take the GE fan control switch and put it in the fan canopy for this purpose. @dalec can say more about that.
But the reason you’re not finding anything about using the Fibaro dimmer to control the fan is that that would be a safety hazard.