Best to check the websites nearer the time - or give them a call.
I went to most of FKK clubs in frankfurt near new year (Dec 2019). Unfortunately most of those clubs except for FKK Sharks were quite empty with not a lot of girls. I went to Manhatten, FKK Oase and Sharks. Sharks had a good 60+ girls but both Manhattan and Oase were pretty low ok volume.
I asked one of the girls - she told me that most girls (coming from other european countries) go back home to spend christmas and new year with their family. Hence low volume