Got a reply from Xiaomi global support: "I would like to inform you that every device is designed as per the basic requirement of a specific region. Hence, we are unable to assure you regarding the working."
Same problem here.
Both the Temperature and the Humidity Monitor and the Gateway (v3) are available in the Portuguese store but the sensor is not shown on the possible child devices list.
If botht products are sold in Portugal and my region is set to Portugal, Xiaomi must make this sensor...