Orphan works are potentially covered by copyright but with no obvious rights holder. As a result, even if you want to publish/show/play them, you’ve no way to request permission but doing so without permission risks copyright infringement. Back in 2005, Duke University’s Center for the Study of the Public Domain discussed the problems this creates for preserving films: thousands of yards of film are decaying but who’s going to spend money preserving something you have no right to show?
Over in the European Union, you can get past this by making a diligent search for the copyright holder. Unfortunately the law is unclear on when you’ve been diligent enough, and even meeting the minimum standard can be difficult.
All but the last 10 Sherlock Holmes stories are public domain. However the Doyle estate argues Netflix’s new Enola Holmes series about Holmes’ brilliant sister infringes on the final 10 by showing Holmes as a complex emotional human being instead of just a thinking machine.
Some companies have tried using trademark as a way to control material that’s now out of copyright. One Supreme Court decision from 2003 says that’s not going to fly.
Self-published authors and fanfic-turned-pro authors are increasingly using copyright law against their competition in dubious ways.
For an unrelated illustration, here’s TYG comparing the size of the onion we got last week to Trixie’s head.