Toon thermostat: humidity sensor not detected?

I’m using the Toon Thermostat integration for my Boxx thermostat from Engie (same HW, same API, different country).
In the Boxx mobile app and on the thermostat I can also monitor the humidity of the room. However in Home Assistant I’ve not seen this sensor (also looked at the hidden ones). Has anyone been able to add this sensor manually?

I’m trying to find an answer for this too…