Good way to get the engine info. Unless you have a specific problem ,such as heater not efficient, then I would not worry about it . Diesel engines usually run a little cooler than the petrol models.

There’s a secret menu on these which shows the exact temperature. I don’t know what it was running at before though.

The question that always comes to me is - the temp may be 'exact', but is it accurate ? That will need a sensor of some sort sending a signal to an electronic display; either one may introduce inaccuracy. If it always reads the same, at least the system is stable. If the readout starts to vary, that is the time to worry. Do you get heat after a few miles driving ?

My diesel runs at a displayed 90° by the way (gauge, not digital).