Lufthansa at least has Rail & Fly where for €60 return you can add a DB train ticket to the flight. The ticket gets you from anywhere to the airport and back. Since the train and flight are booked on the same ticket, if there is a train delay (or flight delay returning) you will get rebooked on the next flight as if you had taken a flight. It's pretty great, I would recommend it.

https://www.lufthansa.com/de/en/rail-and-fly