This has been an issue in my car when I'm not using it regularly or taking it for longer drives. Because it sits outside the interior of the car tends to absorb humidity on the seats and carpets and roof liner, so when you first get in it the heater is heating up the fabrics and releasing that stored up humidity which ends up on the interior of the windows. If there's people sat in the car the breath does this also. If there's snow or rain on the ground it can come in on your shoes and sit on the floor too and it'll never evaporate if you only take short trips or trips with the heater off.
Been having a bit of a play with a hydrometer in my car after it was standing for months, was surprised to see it rising as the heater comes on when heating cold exterior air should drop the humidity significantly (5% for every 1c gained). Figured out that was why.
Go for a long drive with the heater on full (set to exterior not recirculate) and the windows slightly open or block it in on the driveway and let it idle for an hour in the same way, you can get the interior bone dry this way and it will be less of an issue.
