If you want to know if they will be active during the january transfer window then you need to follow them on their official social media handle. Talking about Dortmund performance, indeed i would say they have been impressive this season. I am not against the way they played in the bundesliga. But in the champions league they performed well because they played against a very competitive teams over there. Still they were able to manage and qualify tor the next round. That alone is enough to impress their fans.
Finishing nat the top of their group nis worth commendable as against PSG which came second, Dortmund was in a group that was relatively tough but they finish top regardless of the fact that their point difference was small tho Dortmund has been really brilliant so far I'm their champions league games.
By January transfer window Dortmund may likely be active but for now there have been no formal news I'm that regards, but Dortmund nis usually known for selling off their players I don't know if they will be doing such by January or they will wait till the end of the season but then I'm yet to see any of the players they will be willing to sell then, they my not have much to sell off this season because they seem like they are aiming at the title this season unlike other times when they just want to be at a good position on the table and probably train players sell and make good money, they show little to no concern with the league title.