In 2021 the company that holds the rights to Dr. Seuss books, founded by his family after his death, announced that they would stop printing several of his books because they judged them to be racist against nonwhites: https://apnews.com/article/dr-seuss-books-racist-images-d8ed... . This isn't a government ban on the content of the books, but rather the legitimate copyright owner refusing to print them for their own ideological reasons.

Once the books go out of copyright they will no longer be able to legally prevent anyone else from printing the books, and copyright law doesn't prevent people from legally reselling their already-purchased copies of books. But if you go onto Amazon right now and look at prices, you'll find that a copy of one of the Dr. Seuss books that the rights-holder refuses to print more copies of, such as McElligot's Pool, costs over 100 dollars; whereas a Dr. Seuss book that the rights-holders haven't judged as racist, such as The Cat in the Hat, costs about $5.