The Naturistenweg Undeloh in Wesel, Undeloh, in the forsts of the Lüneburger Heide
Been there in 2020. The forest is nicer than some suggest.
On busy moments it does attract men looking for more than just a walk
Some parts are shared with regular biking and hiking trails
Areas where it is tolerated:
Forests around Süsing, close to Lüneburg, are mentioned most ofthen. Next to the forest there is also a FKK domain and hiking nude seems to be fully accepted by the locals as long as it is in the forest.
Lots of FKK beaches along the Ostsee, those stretches are sometimes long enough that they are suited for somhiking.