Public domain can get weird. The works of Mozart are obviously public domain. But if I record myself performing some of them, that recording is copyrighted. It doesn’t stop you from doing the same, which would also be copyrighted. Now let’s say I add a few of my own touches to my performance- which would be a derivative work. You cannot copy those in your own performance without my permission. In effect, it’s the changes themselves that are copyrighted.

Once I’ve made my recording, you can face an uphill battle to prove that you either didn’t know about mine, or that it was so obvious that it wasn’t creative.

All of this ignores trademark law, which is related but distinct.