The ferry between Puttgarden and Rødby has two good alternatives. These also take you towards Lolland, Falster, Sjælland, Copenhagen, and Sweden.
A bit further to the east is the ferry from Rostock to Gedser. This connection takes a bit longer with a duration of 2 hours, but it can be a favorable crossing option depending on your route.
The Rostock-Gedser crossing operates 10 times per day and is also operated by Scandlines.
Another option is to take the Great Belt Bridge, also known as Storebæltsbroen, which connects the Danish island of Funen with the island of Zealand. This bridge is an impressive feat of engineering and is part of the E20 highway. From Germany, you can drive on the highways to Flensburg and then follow the E45 to the Great Belt Bridge. It is a toll bridge where you can provide your license plate in advance to ensure a smooth passage.
Once on the bridge, you can enjoy the beautiful view of the sea and the surrounding islands. Once on Zealand, you can continue your journey to destinations in Sweden, such as Malmö or Helsingborg.