I think Puttgarden–Rødby is more likely. It used to be served by diesel ICE trains and it was really fun to ride onto a big old ferry on one of these unusually short ultra-sleek trains, get off the train, walk a lap around it, then go up to the open-air deck and stretch your legs a bit.

There’s still a direct Hamburg–Copenhagen connection via that ferry, but it’s now a normal Eurocity.