In order to unlock this achievement you must finish 25 Rival events on the newly released track, Nurburgring. It does not matter which version of the track you do this on. An easy way to nab this achievement is to go into rivals, select a time attack on the Nurburgring Grand Prix Circuit, complete one lap. After that, select pause, finish race. On the post-race screen, select restart. Rinse and repeat. The achievement unlock criteria behaves exactly to the rival achievement associated with the Long Beach DLC.
In order to get miles driven towards the “The German Connection” achievement, I would suggest using either an Audi, BMW, Mercedes-Benz, or Volkswagen model vehicle.
I hope this solution helped! Leave a comment letting me know if there is any room for improvement! Thanks.