Until January 1, 1975, German mothers did not pass on German citizenship to children born in wedlock, only German fathers did. A new law took effect on August 20, 2021 to address this kind of historic gender discrimination in citizenship practices, adding a process called Staatsangehörigkeit § 5 by which descendants of German mothers can declare their German citizenship. I wrote about our experience with this process, which we completed in 2023.
The law created Staatsangehörigkeit § 5 with a window of ten years. Germany began accepting these declarations on August 20, 2021 and will continue until August 20, 2031. Today marks the halfway point. Declarations delivered to the Bundesverwaltungsamt (BVA) by August 20, 2031 will be processed, even if the processing continues past that date. If the declaration is not presented to the BVA by then, the opportunity is lost.
If you were born to a German mother/grandmother/etc prior to 1975 and a declaration of German citizenship is something you'd consider doing, I'd advise starting on it soon. The right to do this extends to subsequent generations: descendants of the ancestor denied citizenship, children and grandchildren and so on, can all declare their citizenship. Reddit's /r/GermanCitizenship is a good resource for help, with a guide of the various pathways to citizenship.