As such most-if not even nearly all, are indeed ICE-sets from DB IN Germany. Check timings for main airport-stops like FRA for nighttime-as in fact most re aimed to serve that for very early flites and very late arrivals.
New since this yr are the 2 NightJets-with the complete offer, which however also include a 3-4 cars -seat only- labelled as IC, to Basel from AMS and from Hamburg.
For shorter distance: In the Rhein Ruhr area-mostly weekends, are a fair lot of RE-routes that do run 24 hrs and also nearly ev hour nighttime-also a few S-bahne. A bit less on weekdays-and then again mostly aimed to bring pax and workers early to airports (DUS and CGN=Köln/Bonn)
DSB in DK has also the odd IC running nighttime-seats only, like K/obenhvn-Aarhus/Aalborg and/or Esbjerg. A kind of remnant from old times (when it was by ferry they also had couchette).
In summertime the overnight K/obenhavn-Haburg is seat-only, consist of just 2 DSB 2-car sets and needs Reservation-last summer hopelessly overcrowded by INterrailers and Swedes in transit.