It doesn't need to be at the dew point inside, if it's a few degrees lower we already win a ton. The 21°C is really just comfort, buildings will be fine at 15°C just as well.

We recently got a dehumidifier for a room that we aren't using most of the time. Better put some greenwashed kWh into taking moisture out of there than burning gas with the conventional heating system to keep the room hot (and it would still be too wet).