Many people ask this question nowadays. Sorry usenet scene was hit hard by german authorities early this year. Most german forums closed down as a precaution after the raid. Most of them never returned online.
So are there sites still left?
Yes, there still are german boards which are operating again.
Brothers of Usenet is still around and then there is House of Usenet.
Personally these community driven forums upload their own german content and list externally uploaded content too. They are well-sorted but generally these forums look like the work of some script-kiddies. They are no comparision to professional indexers, which are way more comfortable and come with an API.
Be careful with these boards because the german authorities might be looking after them at some point again.
It is definitively recommended for germans to visit these boards with a VPN and not use your normal Gmail account for registration. Instead use some kind of temporary mail provider or email hosts that take privacy seriously. Protonmail is one of them and as a company outside EU jurisdiction it is much harder for german authorities to get extract information about the mail account (even in case of a criminal investigation about rather harmless stuff like violation of copyrights for personal usage).