The internal pull-up is relatively high, probably somewhere around 100K ohm. I didn’t know it wasn’t sufficient for some cases. Can certainly add a strong pull-up in the future version,.
The internal pull-up is always on — the firmware turns it on right at the initialization step. You can verify this by checking the sensor port to ground voltage (assuming no sensor is connected to interfere with it). The voltage should be around 3.3V, if so that means the internal pullup is on.