We will be in the Black Forest in mid January. Any insight to what is the best things to see then? No hiking of course.
The weather will be terrible.
https://www.holiday-weather.com/black_forest/january/2021/
It will be cold, near freezing. If you go then, you will face short, cold days.
Why go in January?
I agree it's not the most ideal time to go. I was in Baden-Baden in early March and it was dreary although not terribly cold by then. If you must go in January, maybe spend time in the neighboring cities to warm up and spend time indoors at interesting sights to break up your driving? Baden-Baden is famous for its thermal spa and casino. I've heard good things about Freiberg but haven't visited there myself.
Actually some winter hiking/walking on a cold clear blue sky day can be a good thing in the Schwartzwald. I'd pick an area with access to a café/restaurant or two. Dress warm and for snow. Around the Titisee, take a lift up the Feldberg (ski season), a hike up the Triberg Falls (snow and path allowing), some sled riding, snowshoes, cross-country skiing etc? Have a nice honey Schnapps sitting near the fire or Kachelöfen.