In Germany a work can only enter the public domain after the copyright expires. The author is not allowed to waive their copyright and intentionally put their work in the public domain before that. If you want to make something available without restrictions you have to grant people a license to your copyrighted work.
One of the things that is different is the matter of Moral Rights such as the right to be attributed as the author of the copyrighted work. In some jurisdictions those rights cannot be waived. https://en.wikipedia.org/wiki/Moral_rights